Abstract： The steady cavitating flows of NACA66 hydrofoil were investigated numerically based on the RANS equations of homogeneous multiphase using high quality multiblock structure grid, combined with SST k－ω   turbulence model and Z-G-B cavitation model. Numerical simulation results are in good agreement with the experimental data. Consequently, it is indicated that the numerical simulation method is applicable and reliable. Furthermore, URANS equations and sliding mesh method were applied to the numerical predictions of unsteady cavitation performance for pump-jet propulsor on UUV. The results show that the numerical simulations accurately predict the cavitation inception and extension, shape and location. When cavitation phenomenon appears, the efficiency of pumpjet propulsor drops significantly, even  up to more 20%. The obtained pressure distributions of UUV surface, rotor and stator blades are reasonable and consistent with the cavitation phenomenon. Additionally, the pressure difference of pressure side and suction side of rotor blade causes tip vortex and tip clearance cavitation, which result in a further drop in efficiency of pump-jet propulsor.