He assumed the titles General Fuhan ("assisting Han") and Governor of Shu Commandery and of Yi Province (which included most of modern Sichuan, Chongqing, Guizhou, and Yunnan).

[4][5] In the fourth month (May or June in Western calendar) of 25 AD,[4][5] Gongsun Shu declared himself emperor in defiance of Gengshi,[2] whose throne was being threatened by the forces of Liu Xiu.

[6] Gongsun Shu sent general Hou Dan (侯丹) to take over Hanzhong in the north and Ren Man (任滿) to Jiangzhou (modern Chongqing) to the east, and took control of the entire Yi Province of the Han dynasty.

[6] Other rebel forces who were defeated by Emperor Guangwu, most importantly Yan Cen (延岑) and Tian Rong (田戎), also submitted to Chengjia.

[4][6] At the time, Emperor Guangwu was embroiled in the civil war engulfing much of China, and Gongsun Shu's advisor proposed attacking Han while it was still weak.

[5] Chengjia remained independent for more than ten years, owing to the natural defences enjoyed by the Sichuan basin, and the unsettled conditions in the newly established Eastern Han.

Wounded in the battle, he died in the night, and the defenders of Chengdu under Marshal Yan Cen surrendered the following day, marking the end of Chengjia.

[2] Gongsun Shu modelled his government after that of the Han dynasty, and appointed his advisor Li Xiong and his younger brothers, Guang and Hui, as the Three Excellencies.