Abstract: In order to study the first stage impeller cavitation characteristics of the centrifugal charging pump, Pro/E and ICEM software were respectively used as the tools for three-dimensional modeling and meshing of the hydraulic machinery, and a numerical calculation method was determined based on Reynolds time-averaged N-S equations, RNG k-ε two-equation turbulence model, SIMPLEC algorithm and cavitation model, and last unsteady numerical simulation and experimental comparative study of the first stage impeller cavitation characteristics of the centrifugal charging pump were finished. The results showed that: when initial cavitation happened, gas volume fraction less affected the impeller internal pressure; when critical NPSH reached, inlet cavitation changes near the blade has great effect on the pressure; simulation and experimental results of critical NPSH were respectively 7.35 m and 7.58 m, and error was about 2%, and they all satisfied the nuclear power specifications of ≤ 7.8 m.