Abstract: The working state of crank rod system has direct influence on the engine’s output performance. This paper studies a reliability analysis method using Bayesian network to evaluate its reliability and determine the the system weakness. The mapping method is presented to establish the Bayesian network based on the fault tree analysis. The occurrence probability of the basic events and the top event can be calculated by fusing various kinds of prior information by analyzing the effects of each component on the system reliability and calculating the importance measures of each event. The vulnerable parts of the system are found out by the above analysis. An application example is illustrated to verify the effectiveness and feasibility of the proposed method.