For the coolant pump working in high temperature, high pressure and high radiation for a long time in hostile work environment, and its concurrent fault in high probability, a method of DSmT on Decision Level was provided to solve main coolant pump concurrent fault diagnosis problems, and a DSmT identification theory frame for pump rotor imbalance, pump rotor misalignment and spindle damage was built. Then, by using actual measurement data synthetically, DSmT fault features reliability assignment was determined by judging multiple independent evidence sources by DSmT, and then, the diagnosis of main coolant pump failure and its concurrent fault was calculated. The experiment results show that the proposed method can effectively identify the main coolant pump concurrent fault characteristics, and it has some theoretical and engineering application value.