Abstract: Abstract: The impeller diameter is one of the fundamental parameters of double channel sewage pumps. In order to analyze the effect of different impeller diameters on pressure fluctuation, the unsteady characteristics of a double channel sewage pump was numerically simulated by using the Mixture multiphase flow model and the developed standard k-ε turbulence model. The double channel pump mainly consisted of volute, impeller, inlet extension and outlet extension. In order to improve the calculation stability, the impeller totally rotated for 18 cycles in the simulation and the total computation time was 0.3724 s. The simulation results of the last 2 periods were used to analyze the pressure fluctuation in the pump. Monitoring points were set in the middle of each section in volute circumference and in the tongue region so as to analyze the distribution and variation of the pressure fluctuation with the impeller diameter in the volute especially around the tongue. The calculation results were compared with the experimental data when the impeller diameter was 103 mm. The experiment was conducted in an open test platform, and the test measured the hydraulic performance of the pump and the pressure pulsation of the volute outlet. The pump head and efficiency deviation between calculated and experimental results were 2.37% and -0.46% respectively under the design condition, while the errors were slightly larger but less than 5% under other conditions, which illuminated that the numerical model and calculation methods predicted the hydraulic performance of double channel sewage pump extremely well so that it could be used to predict the characteristics under other impeller diameters. The pressure pulsation trend between calculated and experimental results fitted well and the error was small, which demonstrated that the CFD (computational fluid dynamics) method was able to forecast the distribution and variation of pressure pulsation in the pump accurately. The results showed that the pressure fluctuation of volute circumference under the design condition generally got weaker with the addition of certain amount of particles and the maximum decreased by 30.9%, and the average pressure pulsation reduction of the volute circumferential points decreased with the increase of impeller diameter. The results made clear that selecting appropriate impeller diameter could contribute to prevent pressure pulsation and the induced vibration and noise in the pump when transporting solid-liquid two-phase flow. The pressure fluctuation around the tongue got more and more sharply with the increase of impeller diameter when the water included proper amount of particles. The dominant frequency of points near the tongue was almost the blade passing frequency. Compared with water, the maximum amplitude of the reduction of the pressure pulsation increased and then decreased with the increase of impeller diameter, and the maximum reduction was 22.7%. The lower point of these points in the tongue region was affected maximumly by the rotor-stator interaction between impeller and volute. Instantaneous static pressure of every monitoring point fluctuated sharply when impeller diameter increased to 105 mm under solid-liquid two-phase flow. Selecting the appropriate impeller diameter could contribute to weaken the pressure pulsation when transporting solid-liquid two-phase flow. The study indicates that the impeller diameter has a very important impact on the distribution and variation of the double channel sewage pump and it provides the basis for the optimization design of double channel sewage pump.