Abstract: The existence of cavitation is very unfavorable to the operation of the turbine, which will not only reduce the output and efficiency of the turbine, destroy the overcurrent parts of the turbine, but also lead to the unsafe and unstable operation in serious cases. Accurate identification of the cavitation position helps to prevent cavitation damage. This paper uses the VOF multiphase flow model and SST k-ωturbulence model to simulate the Schnerr-Sauer cavitation model. Through an analysis of the distribution rules of the velocity field and pressure field of the gas phase are obtained. The main conclusions are as follows: When the fluid flows through the contraction pipe section, the speed increases rapidly, and the absolute pressure at the outlet of the nozzle drops rapidly to the saturated steam pressure needed to form cavitation, which creates conditions for cavitation. There is a speed attenuation in the center of the injection needle, and a low pressure zone in the nozzle exit and the tip area of the injection needle. The gas phase is mainly distributed at the outlet position of the nozzle. Under the opening of 20% and 80%, the gas phase is symmetrically distributed in the injection outlet torus, but not fully covered, the gasification area corresponds to the position of the anterior fluid diversion area, and the opening of 40% and 60% evenly covers the nozzle outlet. The maximum gas phase generation rate and gas distribution along the axial direction under different injection needle opening degrees first increase and then decrease with the opening degrees. The water vapor content at 40% opening degree is the most, and the cavitation range at 40% opening degree is the largest