Abstract: Based on the complex network theory，a reliability network model of urban rail transit system is established，and a system reliability evaluation method based on Bayesian network reasoning is proposed. In which，to solve the problem of non quantifiable parameters in calculation，a method of decentralization is proposed. The modeling and calculation results of urban rail pantograph system show that the reliability evaluation method based on Bayesian network can be used as a practical modeling and the analytical method，which can be applied to the reliability analysis of urban rail train mechanical system.