In order to study the effect of different impeller outlet widths on the unsteady performance of centrifugal pumps under design conditions，a centrifugal pump with a specific speed of 66 is selected as the research object． The numerical simulation of centrifugal pump models with impeller outlet widths of 11，12，13，14 and 15 mm is conducted． An analysis is made of its external characteristics，internal flow field，and the variation of pressure pulsation． The results show that the impeller outlet width has a significant effect on the external characteristics of the centrifugal pump． The larger the outlet width and the higher the lift，there is an optimal impeller outlet width so that the centrifugal pump has the highest efficiency under the design conditions，ie，b = 14 mm． With the increase in outlet width，the pressure of impeller and volute increases，the area of low velocity area in the impeller flow channel increases，and the turbulent kinetic energy decreases． The pressure pulsation amplitude of the monitoring point in the scroll flow channel increases with the increase in the impeller exit width． The pressure pulsation amplitudes at the monitoring points of the lapped tongue and the exit point first decreases and then increases with the increase in the outlet width，and the pressure pulsation amplitude is the lowest at b = 14 mm． A comprehensive analysis shows that there is an optimal impeller outlet width to optimize the performance of the centrifugal pump，which provides a certain reference value for the centrifugal pump hydraulic design with a specific speed of 66．