According to the strictly real-time demands for safety state detection of EMUs, safety status detecting network of EMUsbased on the heterogeneous network that consists of switched industrial Ethernet and CAN bus was studied. In order to satisfy the real-timeperformance of the network, the worst case network delay of the periodic messages was analyzed, and the analysis formula of delay in worstcase was deduced. It was clear that the main factors affecting the worst case network time delay were the number of CAN nodes, Ethernet/CAN gateways and vehicle level switches based on the analysis formula. The trends of the worst case network delay with the changes of CANnodes, Ethernet/CAN gateways and vehicle level switches were analyzed, and the analytical model was validated by simulation. The worstcase network delay model provided a theoretical basis for the quantitative analysis of network performance. The modeling methods andconclusions could be generalized to other rail traffics.