Abstract: In order to research the pressure fluctuation characteristics of flow field of mixed flow nuclear primary pump,this study used the technique of ANSYS-Workbench and CFX fluid solid heat coupling to do numerical simulation analysis for model pump.According to the situation of pressure fluctuation of time domain and frequency domain,the main cause of pressure fluctuation was discussed.For different flow,the pressure fluctuations were compared.This study shows it is feasible that large eddy simulation method is used for the research of pressure fluctuation.The pressure fluctuation amplitudes of four sections are increasing from wheel hub to wheel rim.The pressure fluctuation of inlet and outlet of impeller depends on the rotational frequency of impeller.Along with the fluid flowing away from the impeller,the effect of the impeller on the fluid pressure fluctuation weakens gradually.Comparing the different results of three flow conditions,the pressure fluctuation in design condition flow is superior to the others.