Aiming at the problems that the faults of NPP’s main coolant pump are difficult to recognize effectively during their early phases, and that DST can only solve single fault diagnosis in the identification framework without serious conflict, this paper proposes a diagnosis model for main coolant pump’s concurrent fault fusion in early phases, based on DSmT. Taking advantage of DSmT, multiple independent proofs are used to conduct fusion decision, and obtain the results of main pump fault and concurrent fault diagnosis. On the simulation machine of nuclear power plant, main coolant pump was simulated and verified, and the results show that this method can improve the accuracy of recognition of main pump’s current faults during early phases, and reduce the uncertainty of the diagnosis.