Sima Yan was only 29 years old when he ascended the throne. Sima Yan, the eldest son of Si Mazhao, the son of Sima Yi and the powerful minister of Wei. On February 8, 266, Sima Yan forced Cao Huan, Emperor of Wei Yuan, to become a Zen master. Acceded to the throne, set the country as gold and changed the yuan to the first year of Taishi.
Sima Yan became emperor at a young age, mainly because his grandfather Sima Yi made preparations for Sima Jia's usurpation from the beginning and made a lot of efforts. Wei regime has been in Sima Jia's hands since the change of Gaopingling in Sima Yi's later years.
After Sima Yan proclaimed himself emperor, in order to consolidate the state power, he put forward the general plan of governing the country by doing nothing. He established a system of three provinces and six departments in governing the country, and also set up a center in Zhongshu Province to participate in political affairs. In this way, the three provinces replaced the system of three public officials and nine ministers in the Han Dynasty. At the same time, it also widely sealed the kings and consolidated the rule of Sima family.
Moreover, after the destruction of Wu, a new law was promulgated, requiring officials not to occupy land and population, and stipulating that descendants of clans should do the same. But at this time, he gave the clan the privilege of owning potatoes economically and exempted the corvee. Therefore, since the Han and Wei Dynasties, the aristocratic families with rising status eventually became the most special class and the most active political force in the Jin Dynasty.
Militarily, Sima Yan dispersed the state and county troops. However, Sima Yan has also enacted a more tolerant law. During the reign of Sima Yan, it can be said that China was reunified from the Three Kingdoms Rebellion, which created the prosperity of Taikang. So Sima Yan was one of the few wise emperors in Jin Dynasty.