Abstract: In order to solve the problem of excessive vibration for a double-suction centrifugal pump in a petrochemical corporation, the influence of impeller diameter on the characteristic of pressure pulsation near volute tongue was studied. Reynolds-Average Navier-Stocks method with sliding mesh technology was used to analyze the unsteady flow field and pressure pulsation in different conditions. The results of pressure pulsation before and after impeller cutting were compared to illustrate the effect. The result indicates that the amplitude of pressure pulsation is positive correlated with flow rate. The blade passing frequency dominates pressure pulsation in different conditions and different impeller diameters. With the increase of the cutting amount of impeller diameter, the amplitude of pressure pulsation shows a decreasing trend. The research shows that cutting impeller diameter is an effective way to improve the pressure pulsation.