The aircraft AC power generation system is the key subsystem of the power supply system and the main source of power for the whole aircraft, so a complete safety analysis is required. Methods such as fault tree analysis, failure mode and effect analysis are used for traditionally safety analysis, and less attention is paid to safety issues caused by nonlinear interactions between system components. The article introduces the basic structure of the AC power generation system of a typical large passenger aircraft, using the method of combining system theory process analysis and the theory of timed automata formal analysis, build the safety control structure diagram of the AC power conversion process, identify Unsafe Control Action (UCA), and generate relevant causal scenarios by integrating Failure Mode and Effect Analysis(FMEA), combined with formal tools based on the theory of timed automata for system modeling and UCA verification. The comparison with the accident investigation results of typical power system shows that the method used can effectively identify the cause of the accident and conduct a comprehensive analysis, which can be used as an effective supplement to the traditional safety analysis method of aircraft power system.