In the design of fishway, water supply and energy dissipation pool is usually set up at the inlet section to increase the flow velocity of fishway and strengthen its ability of attracting, collecting and accommodating fish. The mixing of the water from water supply and that from the energy dissipation pool causes obvious disturbance to the water in the fishway, which leads to the flow disorder in the fishway (the part at the energy dissipation pool). In order to completely capture the small scale yet complex turbulent flow field structure and obtain the distribution of turbulent kinetic energy suitable for fish migration, a three-dimensional numerical model was used to simulate the complex three-dimensional flow field of water supply and energy dissipation at the fishway inlet of a power station, so as to solve the turbulent kinetic energy parameter and optimize the water supply and energy dissipation scheme of the cover plates. The results show that when the cover plates are set up on the top of the energy dissipation pool, the water supply flow enters the fishway through the gap between the cover plates, forcing the large scale turbulent vortices to break down to small scale vortices. When the size of the vortex becomes smaller, the viscous shear stress is easy to transform the turbulent kinetic energy into internal energy and dissipate it, so that the turbulent kinetic energy in the fishway decreases. In addition, by adjusting the width of the seams between the cover plates, the outflow of water supply become relatively uniform, and the turbulent kinetic energy can also be reduced. When the seam type is set as narrow at both ends but wide at the middle, the vertical velocity of flow in each seam is uniform, which is conducive to fish migration. This calculation results can provide theoretical basis for the inlet design of similar fishway facilities to obtain a stable and uniform water supply flow and improve the fishway efficiency.