Abstract: This paper presents a numerical investigation of hydrodynamic radial force of mixed-flow pump, through validations and CFD simulations under several flow rates, the global performances of the mixed-flow pump is accurately predicted with RNG k-ε turbulence model, the head prediction error is less than 4.4% under all the operational conditions. The recirculation between the impeller and diffuser dominates the flow passage at part-load conditions, the pressure amplitude at 4 times shaft frequency was bigger than other frequencies, it increased sharply while the flow rate changed from 0.6 to 0.4 nominal flow rate, these demonstrated that the rotor-stator impeller blade passing excitation strengthened the pressure amplitudes of points between the impeller and diffuser under part-load conditions. The transient hydrodynamic radial forces of impeller present a periodicity change with time, the average value of transient radial force is close to zero under a uniform inflow condition. The FFT spectrum analysis of radial forces demonstrated that the amplitude of hydrodynamic radial forces under part-load conditions are much higher than nominal condition, especially at 1 time and 4 times shaft frequency, these phenomena are mainly attributed to the hydraulic imbalance of rotor, rotor-stator impeller blade passing excitation, rotor-stator blade interaction excitation and etc. Based on the analysis above, it is concluded that the recirculation flow pattern under part-load conditions has a significant influence on pressure fluctuation and hydrodynamic radial force.