In order to study cavitation characteristics of a centrifugal charging pump in nuclear power plant，the first prototype was specially made. Pro/E and ICEM software were respectively used to be the tools of three-dimensional modeling and meshing of the hydraulic machinery. The cavitation was divided into four stages: cavitation inception，cavitation development，critical cavitation and fracture cavitation. Based on SST k-ω turbulence model，cavitation numerical simulation was finished by ANSYS CFX software. The results showed that: with the occurrence of cavitation，number of bubbles in the radial position in the impeller increases rapidly，and bubble volume fraction is also growing. Vortex appears gradually in the impeller and it leads to sharp decline in pump head in fracture cavitation. （修改后：When cavitation occurs to a certain extent, vortex appears in the impeller and its area constantly increases.）Pressure pulsation is regular in cavitation inception and dynamic and static interference of the impeller and the volute plays a main role；then cavitation gradually becomes the main factor of controlling pump pressure fluctuation rules. In the maximum flow rate condition，head error of simulation and experimental results is 2.1% and NPSH error is 3.5%. The change trend of numerical results and test results are same and they reveal changes of internal flow field of the charging pump indifferent cavitation conditions.