The main workshop structure of nuclear power plant has the characteristics of uneven distribution on mass and stiffness. It is important particularly to research the elastic-plastic seismic response analysis on the main workshop to ensure the normal operation of power plant in rare earthquake, prevent serious property damage and casualties caused by major equipment damage and nuclear leakage. Taking a practical project as the research object, this paper used the large general finite element software ABAQUS, in which the fiber model was used, to research the structural seismic performance under rare earthquake and the deformation and mechanical characteristics of elastoplastic model throughout the earthquake effect, then the effectiveness and feasibility of the method was verified, on the basis of the structural dynamic characteristics and response spectrum analysis. The analysis results show that the structural maximum interlayer displacement angle can meet the demands of 1/100 limit； the seismic fortification standard of “no collapse under strong earthquake” can be achieved in rare earthquake with Ms7.0, which can provide important basis for the seismic design of main workshop structure in nuclear power plant.