In order to ensure the successful on-orbit scientific test mission of TianTou -5 satellite, the possible risks of each component of the satellite propulsion system were systematically and comprehensively evaluated from the perspectives of incidence and severity by using failure mode and impact analysis methods. According to the working characteristics of the satellite propulsion system, a set of fault detection and location methods were proposed according to its on-orbit working state and standby state respectively. The effectiveness of the method is verified in the on-orbit practice, and the healthy operation of TianTuo -5 is successfully guaranteed, and valuable experience is accumulated for the fault diagnosis of the satellite propulsion system in the future.