Abstract: The characteristics of urban rail transit FAO (fully automatic operation) vehicle system are introduced. The current situation of FAO project vehicle system hidden hazard preliminary analysis is analyzed. Based on the standards and specifications related to RAMS (reliability, availability, maintainability, safety), a set of hidden hazard preliminary analysis methods is proposed, including hidden hazard identification, risk assessment and risk control. This method will be applied to a FAO project, where the top-level hazard of the vehicle system will be analyzed and the risk elimination and control measures will be obtained, laying foundation for ensuring system safety.