The present method of calculating equivalent failure probability did not take into account the influence of noncritical state of components on the reliability of valve system,which leads to insufficient reliability evaluation results. Therefore,a new calculation method of equivalent failure probability was proposed in this work. The failure probability data considering the difference of failure consequence were obtained by comparing the failure data with equivalent fault coefficient in Failure Mode and Effect Analysis（FMEA）. On this basis,Markov model and mathematical expectation method in probability theory were used to obtain the expected state transition times,and combined with the existence probability of all states. The failure probability data of non-critical state influence of components were quantitatively analyzed. The key components of the system were determined by the equivalent failure probability of parts and components using the method of Birnbaum importance calculation and analysis. The results show that the equivalent failure probability calculated method is better than the traditional that,in same condition.