Safety analysis is a key task in the development of functional safety of vehicle electrical and electronic systems，and is the primary means of defining hazard identification and safety requirements. Comparing the commonly used safety analysis methods，the automatic parking system（APA）is taken as an example to introduce a system theory based process analysis（STPA）method. By defining relevant hazard lists and control models，analyzing the unsafe control behaviors and causing scenarios that lead to these hazards，defining and updating safety constraints and requirements，and elaborating the STPA approach with the expected functional safety technology for autonomous driving（SOTIF）relationships，it can help to develop functional safety for complex electronic and electrical systems and self-driving vehicle systems.