Abstract: In order to research thermal shock characteristics of the containment spray pump in a 1 000 MW nuclear power plant, the internal flow field of the containment spray pump under thermal shock was calculated numerically. The radial force becomes larger and larger gradually, the fluctuation of radial force is acute, and the axial force becomes smaller and smaller gradually. The fluctuation trends of the radial force and axial force under thermal shock are accorded to the forces in the normal isothermal condition. The temperature loadings which were solved by the internal flow field simulation and the pressure loadings were loaded on the pump’s structure to analyze temperature distribution of the rotor system under thermal shock, and the rules of the thermal stress and mechanical stress distributions. The results show that the thermal stress is predominant destruction factor of the structure. The destruction of the structure caused by thermal stress focuses on the hub, but the mechanical stress destruction concentrates on the boundary of the hub and the vane. From the blade root to blade tip, the thermal stress and mechanical stress of impeller blade decrease gradually.