Abstract: The primary loop system of pressurized water reactor (PWR) consists of reactor pressure vessel (RPV), steam generator (SG), reactor coolant pump (RCP), pressurizer, surge line and other crucial components. The seismic response of each component is closely related to the structure of the whole system. From a system perspective, the primary loop system of the advanced passive pressurized water reactor was studied. With ANSYS software, the three-dimensional finite element model was built to perform modal analysis. Based on the results of modeling, the seismic spectrum analysis with three orthotropic directions on the primary loop system was conducted to obtain the stress and displacement response. Then sensitivity analysis of parameters, such as spectrum input angle and stiffness of supports was performed, giving guidance on further design and analysis. Moreover, direct integration method was used to get time-history response, which was compared with spectrum simulation results. The displacement and acceleration input for seismic analysis of specific components were offered. Besides, compared with three-dimensional finite element model, the lumped mass model of the primary loop system was also built to conduct seismic analysis, giving the advantage and necessity of three-dimensional modeling. The study provides technical support for the structure analysis of key equipments of advanced PWR primary loop.