For his merits in the war, in September 306, Sima Mo was appointed Grand General Who Guards the East and transferred to
Xuchang. Two months later, his peerage was promoted to the Prince of Nanyang. In early 307, Sima Yue offered the government position of
situ to Sima Yong, who was able to reclaim
Chang'an and hole up in the city. Yong, believing he had been pardoned, left his city for Luoyang, but when he got to Xin'an (新安, near Luoyang), he was intercepted by Sima Mo's general Liang Chen (梁臣) and strangled to death. On 18 May 307, after Sima Yue moved his base to Xuchang, he also repositioned his brothers to guard key locations. Sima Mo was appointed Grand General who Conquers the West and Chief Controller of
Qin,
Yong,
Liáng and
Yi provinces, and was garrisoned at
Chang'an to replace Sima Yong in guarding the
Guanzhong region. During his tenure, Guanzhong suffered from a great famine and epidemic. Many of Guanzhong's inhabitants began eating each other as bandits ran rampant in the region. Sima Mo planned on melting down copper statues and bronze tripods into cooking utensils to sell them in exchange for food, but his followers advised against it. Sima Yue thought that Mo was not capable in the role he was in, and attempted to recall him to Luoyang, where he would serve as Minister of Works. However, Mo's advisor, Chunyu Ding (淳于定) persuaded his prince to stay, so Mo ignored Yue's order and remained at Chang'an. Yue, who was in the east at the time fighting against the
Han-Zhao dynasty, was unable to take action against his brother. In 309, a native from Pingyang (平陽; in modern Linfen, Shanxi), Liu Mangdang (劉芒蕩) proclaimed himself as a descendant of the
Han dynasty and allied himself with the tribes around Mount Malan (馬蘭山) in
Beidi Commandery to raise an army. Sima Mo sent Chunyu Ding to quell the rebellion, and he had Mangdang and all his followers executed. In early 311, Mo recommended for his son,
Sima Bao to be appointed General of the Household Gentlemen of the West and Colonel of Eastern Qiang Tribes and had him stationed at
Shanggui. The Inspector of Qin province, Pei Bao (裴苞), opposed the decision, so Mo sent his general,
Chen An to attack him. Pei Bao fled to the administrator of
Anding Commandery (安定郡, present-day
Zhenyuan,
Gansu province),
Jia Ya, who sheltered him. The Inspector of Yong province Ding Chuo (丁綽) had previously slandered Jia Ya to Sima Mo, so he also sent another general, Xie Ban (謝班), to campaign against him. Jia Ya retreated to the
Lu River, but he later recaptured Anding and killed Xie Ban with the help of the chieftains Peng Dangzhong (彭蕩仲) and Dou Shou (竇首). He also forced Ding Chuo to flee, so the emperor pardoned Jia Ya and appointed him as the new Inspector of Yong province. ==Death==