Abstract: It is necessary to reasonably determine the SIL (safety integrity level) of professional equipment systems of urban rail transit and to avoid the waste of resources caused by deliberate pursuit of safety functions. In view of accidents that may result in collision, entrapment, fall or even death of passengers due to faults of key subsystems such as train passenger compartment doors, network control and air braking, the safety functions of train that affect passenger safety are evaluated. From the perspective of the safety function of various key subsystems of the train, based on the introduction of risk identification method of HAZOP (hazard and operational analysis), the division of SIL and its evaluation method are expounded. Taking the train of Nanning Rail Transit Line 4 as an example, the SIL evaluation method is applied to actual engineering project to reasonably determine the SIL of each subsystem of the train.