Abstract: The Kaplan turbine is taken as the research object,and five pores with diameter of 4 mm are arranged at the blade inlet to study the effect of blade perforation on the turbine performance. SST k-ω turbulent model is used to do steady numerical simulation of single-phase flow in the turbine with and without perforation at the blade inlet. Based on the convergence,the transient numerical simulation of gas-liquid two-phase flow is carried out by combining the Mixture and Zwart model. The negative pressure zone,bubble area,cavitation bubble volume and vorticity distribution in runner,efficiency and the pressure at the draft tube inlet are analyzed. The results show that the multiphase flow and cavitation model can well simulate cavitation. The blade perforation can effectively reduce the cavitation and vorticity in runner,and has little effect on the pressure fluctuation at the inlet of draft tube and the efficiency of turbine.