Since there are few reliability analysis of Communication Based Train Control System (CBTC) system, this paper presented a comprehensive evaluation method for reliability evaluation of the CBTC system based on the cloud model and the combination weighting method. Firstly, according to the structure and function of CBTC system, the functional hierarchical model of the system was established, and the subjective and objective weights of the underlying equipment were determined by the combination weighting method. The integrated weight value of the system was obtained according to the additive synthesis method. Secondly, the cloud model was used to represent the reliability of the underlying device of the CBTC system. Finally, the similarity between the CBTC system reliability comprehensive index new cloud and the reliability evaluation set cloud model of virtual cloud computing was compared to obtain the final evaluation result. The results show that the CBTC system reliability evaluation method based on cloud model and combination weighting method can correctly and objectively describe the ability of CBTC system to complete the specified functions, which can be used for the research and development and evaluation of CBTC system.