Angu hydroelectric project gains hydraulic head with damming, and applies long tail channels to further increase hydraulic head, which also consider navigation. Utilizing the method of mathematical modeling, this paper carries out the research on technical problems such as increasing hydraulic head and hydraulic navigation condition, etc. According to the relationship between the unsteady flow tailrace water flow movement rule, tailrace hydraulic requirements, wave height, gradient, flow velocity caused by changing load on power plant units and unit opening and closing time, flow rate, this paper puts forward the improving measures, which may serve as reference for relevant professional design.