Based on the complex network theory, this paper established the reliability network model of urban rail transit system, based on system reliability the Bayesian network model is established, and a system reliability evaluation method based on Bayesian network reasoning is proposed. In order 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 analysis method, and this method can be applied to the reliability analysis of the mechanical system of urban rail train system.