In order to study the influence of annular seal exciting force on the dynamic characteristics of multistage centrifugal pump,taking KDY150×8 high pressure multistage centrifugal pump as an example,through the numerical simulation of CFX,the whole flow passage of multistage pump was simulated,and the flow force of the whole flow passage was obtained.The modeling and simulation of the annular seal were carried out,and the fluid leakage with different seal sizes of the annular seal and the radial force on the surface of the annular seal at different whirling speeds were compared and analyzed.The dynamic characteristics of the rotor were obtained by comparing the calculating results of the "dry" state,the"wet"state and the annular seal exciting force.The study results show that the leakage increases gradually with the increase of the annular seal size,and the modified 0.5mm seal size of the annular seal is in the reasonable range.In the"wet"state,considering the influence of the fluid-solid coupling and the sealing force of annular seal,the natural frequency and critical speed of the multistage pumpare increased,especially the first natural frequency,which is increased by 95%.Therefore,in the analysis of the dynamic characteristics of centrifugal pump,the influence of the annular seal exciting force cannot be ignored.