Besides his heritage, Sima Xin was best known for his involvement in the War of the Eight Princes during the reign of his cousin's son, Emperor Hui of Jin, and his death during Zhang Chang's rebellion.
During this period, his mother Princess Dowager Zang died, and he acted appropriately for a mourning son and was thus known for his filial piety.
Sima Xin's staff officer Sun Xun exclaimed, "The Prince of Zhao is treasonous, and all under heaven should band together and kill him.
Due to his contributions, in August, Sima Xin's peerage was promoted to the Prince of Xinye, with a fiefdom of 20000 households.
[11] At the turn of the fourth century CE, many refugees entered Yizhou to flee the rebellion, famine and plague in the Guanzhong region.
[12] However, the plan fell through as the refugees, led by Li Te, revolted in Yizhou against the court's order.
Zhang Chang then attacked Jiangxia's capital and forced Gong Qin to flee, placing the commandery under his command.
Zhang Chang also repelled an attack by Sima Xin's general, Jin Man (靳滿).
[16] Soon, Zhang Chang spread a rumour claiming that the Jin court had sent a large army to kill everyone, seeing that all in the south had risen in revolt.
Zhang Chang's general, Huang Lin (黃林), led 20,000 soldiers to invade Yuzhou, but Liu Qiao defeated him.
Sima Xin sent another petition to the court, this time asking permission to set out and campaign against Zhang Chang.