Abstract: According to the safety and reliabilty performance of fuel cell engine, the requirement and influence factors of its hydrogen safety and electrical safety were analyzed, and mainly from the point of hydrogen safety, the fault tree model of hydrogen leak was set up. Considering the fuzzy and uncertain probability of each elementary and middle event, fuzzy theory and fault tree analysis were combined to express each probability, and the fuzzy probability of top event was figured out, then the fuzzy importance of each elementary event was analyzed by fuzzy number median methods,the weakness of its safety and reliabilty was presented, finally several improvement measures were put forward. The results prove that the fuzzy fault tree adopted in this paper is more applicable and effective than traditional fault tree analysis, which can provide a guidance for enhancing the reliable and secure design of fuel cell engine in the future.