Abstract: The vertical slot fishway is an ecological compensation structure that can effectively alleviate the adverse impacts of hydraulic engineering on fish migration. It is of great significance to study the hydraulic characteristics of the vertical slot fishway under reasonable parameters for the construction of economical and effective fishways. Based on the combination of physical model experiment and three-dimensional numerical simulation, the flow field distribution and hydraulic characteristics of the H-typed vertical slot fishway of nine different chamber length-to-width ratios are systematically analyzed under the condition of 1∶20 high slope. The results show that the mainstream flow presents an “S” shape under all chamber length-to-width ratios, with the maximum velocity attenuation rate ranging from 46.4% to 61.3%. It is found that the optimal chamber length-to-width ratio L∶B is 10∶8 for the H-typed vertical slot fishway with high slope. Under this ratio, the flow pattern inside the chamber is favorable, with the mainstream bending towards the right and reaching maximum curvature. Meanwhile, low turbulence area reaches the largest, and the fishway meets the requirements of the energy dissipation rate per unit water body, which is beneficial for fish migration and sail upstream.The research results can provide some reference for parameter selection and hydraulic optimization design of H-typed vertical slot fishway with high slope.