In order to improve the security and reliability of DCS system, a reliability analysis method of output module of DCS system based on interval T-S (Takagi Sugeno) fuzzy fault tree is proposed. Based on the T-S fuzzy fault tree, the interval T-S fuzzy fault tree model is constructed. According to the fuzzy information of the bottom event, the failure probability of the top event and the weak link of the module are calculated. The reliability of the output module and the importance ranking of the components are given, and an example is analyzed with the analog output module of the nuclear power plant. The results show that the method is consistent with the actual situation and can be used as the main supplement of the traditional reliability analysis method.