Reactive powder concrete (RPC) is one of new composite material, which is applied in the pilot project of the railways construction. According to the literature survey and test data report, the major factors which influence the reliability of 32m prestressed RPC girder in railway bridges are given in this paper. Furthermore, combining numerical simulation with finite-element method, the reliability of the prestressed RPC girder is calculated. The results show that the failure probability and reliability parameter can be obtained through direct sampling method and the latin hypercubic sampling method. The reliability parameter of fracture is 3.9 with two methods, while the reliability parameter of deflection control is 4.1 and 4.2 respectively with the two methods, and the reliability parameters meet the demands of norm of railway bridges. Consequently, the RPC is safety to be used in the railway bridges.