Abstract: To study the influence of the upper crown cavity structure on the leakage water characteristics of medium and high head francis turbines, four types of geometric models of the upper crown cavity structure have been established based on computational fluid dynamics (CFD) technology in conjunction with the engineering example of Xinjiang Hongshanzui first-stage power station. Using the SST turbulence model, numerical simulation of different upper crown cavity structures under seven flow rates is carried out with the leakage water flow characteristics, drainage performance of the top cover drainage holes, sealing performance of the seal ring, and drainage performance of the runner cone as the research indexes. The study shows that: (1) The form of upper crown cavity structure affects the leakage water flow regime distribution, with the main differences being at the top of the upper crown cavity and the drain holes; (2) The addition of a rotor pump in the upper crown cavity is conducive to improving the main shaft seal leakage and excessive axial water thrust problems; (3) Compared with the other structures, the upper crown cavity structure containing rotor pump can significantly increase the top cover drainage volume and the outlet water pressure of the seal ring, and decrease the drainage volume of the runner cone; (4) For the application of the roof drainage technology in this power station, it is recommended to use the upper crown cavity containing rotor pump, which can increase the top cover drainage capacity by 38.11% on average, increase the outlet pressure of the seal ring by 45.98% on average, and reduce the discharge volume of the runner cone by 38.90% on average. This paper relies on the application of top cover water intake technology to study the influence of different top crown cavity structures on the performance of hydraulic turbines, which can provide reference basis for energy-saving design of francis turbines.