Criticality matrix analysis is an important method of product analysis and guide improvement measures. In order to solve the situation where experience determines the probability failure mode effect, the designers need to adopt a more practical and objective method. According to the principle and method of quantitative analysis of criticality matrix, the experience reference and ranges of the Failure mode effect probability are collected. Then, the method to achieve the failure mode effect probability based on the fault tree is put forward, and a calculation example is given. The process to determine the probability of failure mode effect is achieved in this article.