Abstract: The flow field characteristics of a main stream are always influenced by the inflow of its tributaries. For a water conservancy project built on the tributary at channel confluence, the layout of the project should be optimized to improve the influence of the discharge flow on the navigable flow conditions at the channel confluence. Based on a water drop project on the tributary of the Paihe reach from the Yangtze River to the Huaihe River as a research object, we studied the navigable flow conditions in the confluence area by means of a 1∶50 scale physical model test, where the discharge of water drop project flows into the main stream at a 90° angle, and put forward the optimization scheme of the project layout. The result shows that navigable flow condition can be improved significantly on the basis of the original layout scheme by the optimization scheme of increasing the discharge flume angle of the outlet section to 10°, symmetrically placing two-stage diversion piers along the outlet section and digging 2 m under the outlet section. Under 5-year and 20-year navigable conditions, the water deflection coefficients are 1.13 and 1.20, respectively, and the maximum transverse velocity in the confluence area is 0.15 m/s and 0.29 m/s, respectively, which meets the navigable requirements. The research results can provide a useful reference for the layout of similar water drop projects.