生平

太寧三年三月戊辰（325年4月1日），晉明帝立司馬衍為皇太子。同年閏八月戊子（325年10月18日），晉明帝去世，翌日五歲的晉成帝即位為帝。由於年幼，由母親皇太后庾文君臨朝稱制，由七位顧命大臣輔政，中書令庾亮以國舅身份主政。。

咸和二年（327年）年末，歷陽內史蘇峻與豫州刺史祖約叛亂，並在翌年率兵攻至建康，庾亮試圖抵抗但失敗，被逼出逃，晉成帝就與王導等眾官為蘇峻所挾持，宮中就遭到蘇峻軍搶掠和焚燒，太官也僅餘下數石米供成帝食用。咸和三年五月乙未，蘇峻強逼晉成帝遷居至石頭城一個倉庫中，成帝哭著登車出發，宮中人們亦都傷心痛哭。咸和四年（329年），以陶侃為首的軍隊平定蘇峻之亂，迎回成帝，因為宮殿遭戰火破壞，故修繕建平園作為宮室，至咸和七年（332年）新建的建康宮落城後才遷去新宮。

蘇峻之亂後，朝內就由王導專制，成帝對王導亦相當敬重，甚至屢幸王導宅第；庾亮則領豫州刺史出鎮蕪湖，主掌軍事，隨著陶侃去世，庾亮更兼荊江豫三州，轉鎮武昌，並著眼對後趙的北伐。咸康五年（339年），庾亮作出北伐部署，上奏移鎮襄陽石城，並且增兵長江、漢水流域以及淮泗壽陽地區要地，為一舉北伐作好準備，當時庾亮更派兵進攻巴郡，攻至江陽，俘獲後趙將領李閎及黃植。晉成帝下給群臣議論，上疏得王導支持，但郗鑒以資源不足為由反對。不過未等到允許，庾亮的行動就遭後趙以軍事行動作回應，派軍大舉南侵，庾亮所定的重鎮邾城更加被攻陷，庾亮北伐遂流產。

咸康二年（336年）晉成帝頒布壬辰詔書，禁止士族、官吏將私佔山川大澤；咸康七年（341年），又以土斷方式將自江北遷來的世族編入戶籍。

咸康八年（342年）7月23日，晉成帝患病，中書監庾冰為了留住潁川庾氏家族與皇帝的血緣親近，於是以國家外有強敵，宜立年長君主為由勸服成帝以弟弟琅琊王司馬岳為儲君。7月26日，晉成帝駕崩，年僅22歲，廟號顯宗。8月18日，葬於興平陵。

性格特徵

• 晉成帝年紀小小就很聰敏，有成年人的量度。蘇峻之亂前，庾亮以謀反罪誅殺了南頓王司馬宗，成帝一直不知，至亂事平定後才問及失蹤的司馬宗，庾亮答稱他因謀反而被誅，豈料成帝卻哭著說：「舅言人作賊，便殺之。人言舅作賊，復若何？」嚇得庾亮恐懼失色。至後來，庾懌送毒酒意圖毒殺江州刺史王允之，被揭發後成帝就怒道：「大舅已亂天下，小舅復欲爾邪？」庾懌被逼自殺。不過成帝年輕時被舅舅家族穎川庾氏勢力所限制，並不親政。至後來長大，卻留心事務，而且生活儉約，曾因射堂需耗用四十金而放棄建造。

• 在石頭城時右衞將軍劉超仍為成帝講授《孝經》及《論語》，但因劉超與鍾雅帶成帝逃出去的圖謀洩漏，二人遭蘇峻派任讓收捕殺害，期間晉成帝抱住任讓哭求：「還我侍中、右衞！」但任讓不聽小皇帝的命令，將二人殺了。蘇峻之亂被平定後，任讓原本因與陶侃有舊情而得免死，但成帝記恨他，任讓還是被誅殺《晉書·劉超傳》。

家世

后妃

• 成恭皇后杜氏，杜預曾孫，咸康二年立為皇后。

• 章太妃周氏，成帝貴人，生司馬丕及司馬奕，哀帝即位後獲尊崇為皇太妃。

子女

• 司馬丕，初封琅邪王，後即位為晉哀帝

• 司馬奕，初封東海王，後徙琅邪王，哀帝死後立為帝，被桓溫所廢

• 南平公主，嫁劉赤松。

• 尋陽公主，嫁王禕之

影視作品

• 唐國強：2007年《赤松山魂》

Family background

Sima Yan was born as the oldest son of Emperor Ming of Jin, who was crown prince at that time, by his wife Crown Princess Yu Wenjun, in 321. After Emperor Ming took the throne in 323 following the death of his father Emperor Yuan, he created Crown Princess Yu empress, but did not immediately create Prince Yan crown prince, until 325.

In fall 325, Emperor Ming grew ill. He entrusted the four-year-old Crown Prince Yan to a group of high-level officials, including Sima Yang the Prince of Xiyang, Wang Dao, Bian Kun (卞壼), Chi Jian, Lu Ye (陸瞱), Wen Jiao, and Empress Yu's brother Yu Liang, perhaps intending that they lead by group with a balance of power. He died soon thereafter. Crown Prince Yan took the throne as Emperor Cheng.

Reign

Yu Liangs regency

Initially, the officials were in charge together, but as Empress Dowager Yu became regent, Yu Liang became effectively the most powerful official in the administration. He changed from the lenient policies of Wang (who was prime minister during Emperor Ming's reign) to stricter applications of laws and regulations, which offended the officials accustomed to Wang's lenience. Further, he became apprehensive of the generals Tao Kan and Zu Yue -- neither of whom was mentioned in the list of honors and promotions announced by Emperor Ming's will and believed that Yu had erased their names from the will—and Su Jun, who had allowed many criminals to join his army. In 326, he alienated public opinion by falsely accusing Sima Yang's brother Sima Zong the Prince of Nandun of treason and killing him and deposing Sima Yang.

The Su Jun Disturbance

In 327, apprehensive of Su, Yu decided to try to strip his military command by promoting him to the minister of agriculture—a position that did not involve commanding troops. After initially hesitating, Su eventually refused and formed an alliance with Zu against Yu. Upon hearing this, Wen, whom Yu had made the governor of Jiang Province (江州, modern Jiangxi) to defend against Tao, the governor of Jing Province (荊州, modern Hubei), wanted to quickly move to help defend the capital Jiankang, as did the local forces to the east of the capital, but Yu declined all help, wanting Wen to remain in position against Tao and believing that he can defeat Su easily. Fearful that Yu would be defeated by Su, Wen headed toward the capital any way, but before that Su was able to capture the capital in early 328 and take Emperor Cheng and Empress Dowager Yu hostage. Bian died in the battle, and Yu Liang was forced to flee to Wen. Su allowed his soldiers to pillage the capital, and officials and commoners alike had their possessions—as well as clothes—stripped by Su's army, which even seized Empress Dowager Yu's servant girls. Empress Dowager Yu, humiliated by Su and fearful of what was to come, soon died in anxiety.

Su organized a new government, with Wang Dao, whom Su respected, as the titular regent, but with Su himself in actual power. Meanwhile, Yu and Wen organized efforts to recapture the capital. Wen's cousin Wen Chong (溫充) suggested inviting Tao, a capable general with a sizable army, to be the supreme commander of the army. However, Tao, still resentful of Yu, initially refused. Eventually he relented and joined Wen and Yu. They advanced east toward Jiankang. In response, Su forcibly took Emperor Cheng to the fortress of Shitou and put him and his attendants under virtual arrest. Meanwhile, Wang was secretly ordering the commanderies to the east to rise against Su, and he eventually persuaded Su's general Lu Yong (路永) to defect with him to Wen and Tao's army as well. Chi also arrived with his forces from Guangling (廣陵, in modern Huai'an, Jiangsu).

The Su and anti-Su forces battled for months, indecisively, and despite the numeric advantage the anti-Su forces had, they were unable to prevail, leading Tao to at one point consider withdrawing. However, Wen was able to persuade him to stay and continuing the battles against Su. In the fall, during an assault on Shitou, the anti-Su forces initially suffered losses, but as Su was making a counterattack against them, he fell off his horse and was hit by spears. The anti-Su soldiers rushed him and decapitated him. Su's forces initially supported his brother Su Yi (蘇逸) as leader and continued to defend Shitou, but by early 329 were defeated.

In the aftermaths of Su Jun's defeat, with Jiankang having been heavily damaged by war, the top officials considered moving the capital to either Yuzhang (豫章, in modern Nanchang, Jiangxi) or Kuaiji (in modern Shaoxing, Zhejiang), but after Wang opposed, noting that Jiankang was in a better position to monitor the northern defenses against Later Zhao, the capital remained at Jiankang. Wen was requested to remain in Jiankang as regent, but he, believing that Emperor Ming intended Wang to serve that role, yielded the position to Wang. Meanwhile, Yu Liang, initially offering to resign all of his posts and go into exile, accepted a provincial governor post.

In light of his mother's death, the eight-year-old Emperor Cheng appeared to have been raised by his paternal grandmother, Lady Xun, from this point on.

Wang Daos regency

In late 329, Wen Jiao died, and the general Guo Mo (郭默) soon assassinated his successor Liu Yin and seized Jing Province for himself. Wang Dao initially wanted to avoid another war and placated Guo, but Tao Kan and Yu Liang opposed, and their forces quickly converged on Jiang Province's capital Xunyang (尋陽, in modern Jiujiang, Jiangxi) in 330, killing Guo.

Meanwhile, during and after the Su Jun Disturbance, Jin forces in central China, without the central government's aid, were unable to hold their positions and eventually lost most of central China to Later Zhao. Key cities lost during this time included the old capital Luoyang, Shouchun (壽春, in modern Lu'an, Anhui), and Xiangyang (襄陽, in modern Xiangfan, Hubei), although Xiangyang was recaptured in 332. In 333, Jin also lost Ning Province (寧州, modern Yunnan and Guizhou) to Cheng Han (but regained it in 339).

As regent, Wang largely restored his earlier policy of lenience and lax enforcement of the laws, greatly stabilizing the political scene but also leading to the spreading of corruption and incompetence. Eventually, in 338, Yu Liang tried to persuade Chi Jian to join him in moving to depose Wang, but after Chi refused, Yu did not carry out his plan.

In 336, Emperor Cheng married his wife Empress Du. Both of them were 15.

In 337, Murong Huang, the Xianbei chief who had been a Jin vassal with the Jin-bestowed title of Duke of Liaodong, claimed the title of Prince of Yan notwithstanding Jin's failure to grant him that title, effectively declaring independence and establishing Former Yan, although Murong Huang continued to claim to be a Jin vassal.

In 339, Yu wanted to make a major attack against Later Zhao, hoping to recapture central China, and Wang initially agreed with him, but after opposition by Chi and Cai Mo, Emperor Cheng ordered Yu not to carry out the war plans. Wang died in the fall of that year, and was succeeded by his assistant He Chong (何充) and Yu Liang's younger brother Yu Bing (庾冰). Emperor Cheng let He and Yu Bing decide most important matters, but also appeared to start making some decisions of his own. Yu Bing and He tried to reform some of the problems with Wang's regency, but did not appear very effective at doing so.

Late reign

After Wang Dao's death, Yu Liang resumed his plans for a campaign against Later Zhao, and this brought a major response by Later Zhao's emperor Shi Hu in late 339. Later Zhao forces inflicted great damage on many Jin cities and bases north of the Yangtze and captured Zhucheng (邾城, in modern Huanggang, Hubei). Humiliated, Yu cancelled the plans for a northern campaign, and he died in early 340.

Also in 340, Murong Huang formally requested that he be granted the title Prince of Yan. After lengthy debates among key officials about whether Murong Huang was still a faithful vassal, Emperor Cheng himself ruled that the request be granted.

In spring 341, Empress Du died. Emperor Cheng would not create another empress.

Later that year, Emperor Cheng decreed that the refugees from northern and central China, who had fled south during the times of Emperor Huai and Emperor Min, who had retained household registrations according to their native commanderies, be henceforth registered with the commanderies that they were now living in. This pragmatic move allowed the local commanderies to have greater manpower and reduced redundancy in local administrations.

In summer 342, Emperor Cheng grew gravely ill. He had two young sons -- Sima Pi and Sima Yi, then still in cradles, by his concubine Consort Zhou. Yu Bing, fearful that the Yus would lose power if a young emperor were named, persuaded Emperor Cheng that in the face of the powerful enemy Later Zhao that an older emperor should be named. Emperor Cheng agreed and designated his younger brother, Sima Yue the Prince of Langya be his heir, despite He Chong's opposition. He issued an edict entrusting his sons to Yu Bing, He, Sima Xi, Prince of Wuling, Sima Yu, Prince of Kuaiji (both paternal uncles), and Zhuge Hui (諸葛恢). He died soon thereafter and was succeeded by Prince Yue (as Emperor Kang).

Era names

• Xianhe (咸和 xián hé) 326–335

• Xiankang (咸康 xián kāng) 335–342

Family

Consorts and Issue:

• Empress Chenggong, of the Du clan of Jingzhao (成恭皇后 京兆杜氏; 321–341), personal name Lingyang (陵陽)

• Guiren, of the Zhou clan (貴人 周氏; d. 363)

　• Sima Pi, Emperor Ai (哀皇帝 司馬丕; 341–365), first son

　• Sima Yi, Duke Haixi (海西公 司馬奕; 342–386), second son

• Unknown

　• Princess Nanping (南平公主)

　　• Married Liu Chisong (劉赤松)

　• Princess Xunyang (尋陽公主)

　　• Married Wang Yizhi of Taiyuan (太原 王禕之)

Ancestry