Emperor Cheng of Jin (Chinese: 晉成帝; pinyin: Jìn Chéng Dì; Wade–Giles: Chin Ch'eng-ti; December 321 or January 322[1] – 26 July 342[2]), personal name Sima Yan (司馬衍), courtesy name Shigen (世根), was an emperor of the Chinese Eastern Jin dynasty.
He became emperor at age four, and soon after his accession to the throne, the disastrous rebellion of Su Jun weakened Jin forces for decades.
He entrusted the four-year-old Crown Prince Yan to a group of high-level officials, including Sima Yang (司馬羕) the Prince of Xiyang, Wang Dao, Bian Kun (卞壼), Xi 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 also 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.
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 (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.
Before Wen arrived, Su was able to capture the capital in early 328 and take Emperor Cheng and Empress Dowager Yu hostage.
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.
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.
In late 329, Wen Jiao died, and the general Guo Mo (郭默) soon assassinated his successor Liu Yin (劉胤) and seized Jing Province for himself.
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.
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).
After protracted debates among key officials about whether Murong Huang was still a faithful vassal, Emperor Cheng himself ruled that the request be granted.
Emperor Cheng agreed and designated his younger brother, Sima Yue the Prince of Langya be his heir, despite He Chong's opposition.