This paper briefly introduced the structure and characteristics of autonomous-rail rapid transit train(ART). Based on the hazard analysis of the top level of the system, taking the derailment hazard of the train as an example, the identification process of the hazard source and safety function of the ART were expounded. Combined with the relevant safety standards of rail transit and road traffic, through the three aspects of accident severity, accident exposure probability and injury avoidance, the judgment and quantitative calculation basis of the safety integrity level of the ART was described, and then the safety integrity level(SIL) of the safety related functions of the intelligent tram was determined; finally, the safety mitigation measures to realize the safety integrity level of the ART were provided.