Abstract: At present, urban rail transit industry has been developing the next generation train operation control(NGTC) system.Due to the lack of sufficient experience or relevant standards in the design of NGTC system, it is difficult to define appropriate security requirements for it by using traditional security analysis methods.This paper applied the system theory process analysis method to the safety analysis of the concept definition stage of NGTC system design, and found some potential hazards which were easy to be ignored in the traditional safety analysis. On this basis, the paper extended the concept of train movement authority(MA) and proposed a new security constraint, which not only improved the security of NGTC system, but also proved the applicability and availability of system-theoretic processes analysis (STPA) in the security analysis of train operation control system.