A two-level operation failure probability model for power system protection is proposed. This model is based on programmable time Petri net（PTPN） for dynamic simulation of protection logic， and fuzzy Petri net（FPN） for probability calculation. It can be used to simulate protection logic as well as to calculate instantaneous failure probability for protection design purpose according to the system operation mode， protection settings and protection logic. It provides a useful reference for the analysis of the probabilistic characteristics of protection actions and the degree of matching of associated system faults.