Abstract: With the vigorous development of clean energy such as pumped storage power stations, there are fewer and fewer superior addresses suitable for the construction of power stations. In this condition, it is difficult to avoid the situation that the side inlet/outlet is connected to a turning tunnel. The space turning tunnel has a turning in both horizontal and vertical directions, which has a great negative effect on the hydraulic characteristics of the inlet/outlet outflow conditions, such as the uneven distribution of the flow velocity of the trash rack section and the uneven distribution of the orifice flow. In this paper, taking Shuicheng Pumped Storage Power Station as an example, the numerical simulation method was used to study the hydraulic characteristics of the side inlet/outlet connected to a space turning tunnel. Then, on the basis of keeping the layout of the space turning tunnel unchanged, the original design scheme was optimized by adjusting the length of the diffusion section, the slope of the floor and the slope of the connecting tunnel. The results showed that compared with the original scheme, the hydraulic characteristics of the inlet/outlet under the optimized scheme were significantly improved. The non-uniformity coefficient of the flow velocity of the trash rack section was reduced by 39.6%~45.1%, and the non-uniformity of the orifice flow distribution was reduced by 58.4%~68.2%. All hydraulic indicators can meet the design specifications. The research results can provide reference for the design of side inlet/outlet connected to a space turning tunnel.