Abstract: The side deep groove hole and submersible hole combined fishway studied in this paper is a new type of weir hole combined fishway designed by referring to the vertical slot structure of the vertical slot fishway. The research and application of this type of fishway is still in the initial stage, and the distribution law of hydraulic characteristics in the pool room needs to be explored urgently. In this paper, based on FLOW-3D software, the numerical simulation models of the side deep groove hole and submersible hole combined fishway and vertical slot fishway are established. Based on the results of physical model tests, the boundary conditions and input parameters are modified. The flow field structures of the two types of fishways are compared and analyzed, and the influence of different types of obstacles on the hydraulic characteristics of side deep groove hole and submersible hole combined fishway is explored. The results show that compared with the general vertical slot fishway, the side deep groove hole and submersible hole combined fishway has obvious three-dimensional flow field characteristics, which can provide more migration paths and resting places for fish, but its “ L ” type mainstream structure will not help fish to sense the mainstream direction and thus affect the success rate of fish tracing. Cylindrical obstacles with smooth curved surface are arranged in the combined fishway of side deep groove hole and submersible hole. The flow pattern in the fishway pool is improved, the mainstream velocity gradient is reduced, the turbulent kinetic energy is reduced by about 33.3 %, and the maximum attenuation rate of turbulent dissipation rate is 82.78 %. In the construction of fishway engineering, smooth curved surface should be used to avoid the structural type of edge or cross-section shape mutation.