Based on RNGk-ε turbulence model and sliding mesh model,a three-dimensional unsteady numerical calculation is carried out for reduced-scale models of reactor coolant pump whose guide vane is located in different circumferential positions. The influence law of circumferential position of guide vane on the pressure fluctuations at the impeller outlet,the gap of impeller and guide vane and pump casing is studied,and influence of circumferential position of guide vane on the downstream flow of guide vane is analyzed. The results indicated that the circumferential position of guide vane had great influence on pressure distribution of model pump. The circumferential position of guide vane mainly influenced the fluctuation range of pressure fluctuation in the time domain graph and the main fluctuation range of pressure fluctuation atα=0? is the lowest; the circumferential position of guide vane mainly affected the energy amplitude of pressure fluctuation in the frequency domain graph and the energy amplitude of pressure fluctuation atα=0? is the lowest. The energy amplitude of pressure fluctuation is the highest at the impeller outlet,but the energy amplitude is the lowest at the pump casing,and pressure fluctuation is mainly caused by the rotor-stator interaction. The frequency of pressure fluctuation is mainly affected by the blade passing frequency at the impeller outlet and the gap/clearance of impeller and guide vane and is only related to the rotational speed frequency at the pump casing. The circumferential position of guide vane had more influence on the downstream internal flow of guide vane,and the pressure distribution and pressure gradient of section 1 atα=0? is more uniform and smaller. The suitable circumferential position of guide vane can effectively improve the distribution of pressure fluctuation in the pump,and then reduce the vibration of the pump.