In c.October 311, after Emperor Huai was captured by Han after the fall of the capital Luoyang in July (Disaster of Yongjia), Sima Mo, who was defending Chang'an, was captured by the Han general Zhao Ran (趙染; who formerly served under Sima Mo), and executed by Liu Can.

[3] At the time of his father's death, Sima Bao was at Shanggui (上邽, in modern Tianshui, Gansu).

He took the title of Prince of Nanyang, and soon became in control of Qin Province (秦州, modern eastern Gansu), partly due to the death of Jia Ya in c.January 313.

In early 320, when the Former Zhao (renamed from the Han in 319) emperor Liu Yao decided to undertake a major campaign to wipe out Sima Bao, Sima Bao's domain happened to be suffering under a famine, and he fled to Sangcheng (桑城, in modern Dingxi, Gansu), ready to flee to Zhang's domain.

Later that year, Sima Bao's generals Zhang Chun (張春) and Yang Ci (楊次) tried to persuade him to execute another general of his, Yang Tao (楊韜) and also to attack a former subordinate, Chen An, who had surrendered to Former Zhao, but who had continued to covertly supply Sima Bao.