Compared with traditional low-standard ship locks, large-section navigable tunnels have the advantages of increasing water resources dispatching, increasing ship crossing channels and shipping. It is necessary to explore the characteristics of navigable flow conditions under the condition of navigable tunnel and study effective measures to improve the navigable flow conditions at the entrance of approach channel of navigable tunnel in steep bay section. However, the existing research results neglect the navigation channel layout in the steep bay section, and it’s lack of theoretical research on improving the flow conditions at the entrance of approach channel of navigable tunnel in the steep bay section. For this, this article studies the characteristics of navigation flow conditions and numerical simulation of water conservancy in steep bay section of the tunnel. Firstly, the physical model of tunnel navigation in steep bay section is designed to ensure the geometric similarity, flow movement similarity and dynamic similarity between the model and the actual situation in steep bay section. Then, the numerical simulation of navigation water conservancy in steep bay section of tunnel is carried out, and the continuity equation and momentum equation in the new coordinate system are given. This article explores the navigation scheme of large cross-section navigable tunnel in order to obtain effective measures to improve the navigation conditions of this section. Finally, the corresponding experimental results and analysis are given.