In CTCS (China Train Control System) level-3 and level-4,GSM-R is the wireless communications system, and it is a platform to transfer security data of train control. As the train control system is safety critical system, once the security data are delayed or lost by GSM-R, an emergency brake will be executed, or even the danger will happen. This paper bases on two different existing GSM-R double layers networks, and establishes the channel and train control system models, then analyzes the relation between the average train number of one cell and the free channel rate and probability of emergency stop. The results show the intercross double layers network can make the CTCS-3 more reliable than co-sited double layers network.