Based on the RNG k—εturbulence model and Rayleigh—Plesset cavitation function, three dimensional turbulent flow fields in centrifugal pump with inducer were calculated and analyzed numerically. The results showed a good prediction of the head drop for five flow rates. The hydrodynamic mechanism of the head drop was investigated through a local and global study of the flow fields. It was found that head began to approximately drop when the cavitation sheet reached the throat between two adjacent blades. The total pressure breakdown caused by cavitation firstly occurred in the upstream region of the impellers, then progressive decreased as the pressure rose in the whole blade-to-blade passage. Meanwhile, the cavity increased the total pressure of local regions, which would move downstream by the development of cavitation.