Abstract: In order to study the influence of the reactor primary circuit on inlet flow field characteristics of reactor coolant pump（RCP）, the combined simplified modeling of the steam generator（SG）, inlet elbow, cold and hot section pipes, nuclear reactor and RCP was carried out. CFD method was used to calculate the flow field of its primary circuit. Comparing the RCP numerical calculation results with the experimental results under the condition of uniform inflow, it can be found that the head and efficiency errors obtained by numerical simulation are within 5%, which verifies the correctness of the numerical calculation method. The porous medium model is adopted in the reactor primary circuit, and the dynamic matching of the pump characteristic curve and pipeline characteristic curve makes the RCP flow rate differ by 0.998% from the rated working condition value of the closed system, and the difference between head and rated working condition value is 3.76%. The two errors are small, so as to realize the dynamic and static adjustment of pipeline resistance. The results show that the circumferential symmetry of the flow in the inlet elbow is destroyed, and the distribution of pressure and velocity is non-uniform. Influenced by the curvature of the elbow, secondary flow is generated under the action of centrifugal force. Compared with the uniform inflow condition, a pair of vortices with opposite whirling direction are formed at the inlet of RCP under the non-uniform inflow condition. The symmetrical distribution characteristics of velocity and pressure are destroyed, and the variation of axial velocity along the circumferential and radial velocity is greater than 80% of the average velocity. Therefore, the numerical prediction method established in this study can provide a theoretical basis for studying the influence of reactor primary circuit on the inflow characteristics of the RCP impeller.