Abstract: Both anti-operation probability and mal-operation probability with different structures used in shutdown reactor trip breaker are analyzed by failure-tree method.In the analysis,mal-operation probability,which is crucial for reactor safety,is especially considered to analyze the effect of shutdown operation reliability of reactor trip breaker.Results indicate that,the structure of 2/4 form reactor trip breaker for the second type is prior to other structures compared with the performance of mal-operation probability and reliability,and the improvement to decrease mal-operation probability should aim at the purpose of decreasing mal-operation probability of driving signals.