Abstract: In order to explore the depressurization effect and optimization feasibility of different upper crown cavity structures of medium and high head francis turbine runners, taking the No. 4 unit of Xinjiang Hongshanzui First-Stage hydropower station as an example, three different upper crown depressurization structure were taken as the research object. Based on CFD technology, the SST turbulence model was used to steady-state simulate three types of upper crown depressurization structures under seven leakage flows, with a total of 21 calculation conditions. The research indicators are the flow regime characteristics of the leaking water, the drainage capacity of the scupper hole, and the pressure on the underside of the main shaft seal. The results show that there are certain differences in the leakage water flow regime in different upper crown depressurization structures, especially the position of the cavity and drain hole at the top of the crown is the most obvious; adopting the combined upper crown depressurization structure with runner pump on the medium and high head francis turbine can not only improve the working performance of the main shaft seal, but also form a stable local pressure at the comb ring outlet and fundamentally reduce the leakage of the upper crown clearance; in view of the water leakage of the main shaft seal of the power station, adding a runner pump in the upper crown channel of the unit can increase the water discharge capacity of the drain hole by 17.12% and reduce the main shaft seal pressure by 15.98%, which can further improve the operational efficiency of the power station.This study improves the single type of depressurization structure and achieves the optimization goal, which can provide a certain reference for the design, transformation and stable operation of medium and high head francis turbines.