A simulation methodology used to model the performance of a wireless data communication system in a communication based train control system is proposed in this paper. This approach is developed within a simulation environment integrating with two simulators, which are BRaVE, a microscopic railway simulator and OMNeT++, a discrete event date network simulator. The architecture of these two simulators and the interfaces between them are introduced. The major challenges and constraints of data communication system for communication based train control systems are discussed and a co-channel interference model is proposed. A performance metric of wireless communication for measuring the system reliability is generated. Finally a case study is carried out to validate the proposed approach. Based on the simulation results in the case study, it can be found when the wireless connection between train and trackside access point is lost, further moving authority will be not able to generated for the trains.