Cavitation is an abnormal physical phenomenon which can be generated in relatively low pressure regions in centrifugal pumps. In predicting and understanding cavitation in the pumps, it is important to secure their efficiency and reliability. The purpose of this study is to analyze the cavitation flows in centrifugal pumps with variable speeds through numerical methods. The Rayleigh–Plesset cavitation model was adapted as the source term for inter-phase mass transfer in order to predict and understand the cavitation performances. The Reynolds-average Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was accounted for turbulent flows. The numerical analysis results were validated with experimental data and it was found that both results were in good accordance. The cavitation performances were obtained for variable speeds with different temperatures and the effects on cavitation were described according to different cavitation numbers. Cavitation performances were also observed for different centrifugal pump stages (1st and 2nd). The performances of cavitation decreased with the increase of rotational speed. In addition, the development of cavitation is elucidated according to the different temperatures, and the effects of water vapor volume fraction are discussed.