Abstract: A three-dimensional nonlinear FEM model of reactor equipment and system was built. In the model, global Rayleigh damping, local material damping and element damping were used simultaneously to deal with the damping difference of different structures, and the method of equivalent stiffness and equivalent gap between fuel assemblies and the core shroud was proposed. Meanwhile, the contact effect with a positive gap between two concentric cylinders and the dynamic friction effect with variational pre-tightening force was simulated. Subsequently, seismic time history inputs compatible with both response spectrum and power spectrum density（PSD） was introduced as the analysis input, and a nonlinear 3D reactor equipment and system seismic analysis was carried out. Finally, seismic responses were obtained for SSE event. The research in this paper provides a guidance and reference for the future 3D nonlinear seismic analysis of reactor equipment and system.