Based on RNG k-ε two equations turbulence mathematical model of VOF method，we carry out the three-dimensional numerical simulation of flow pressure characteristic and downstream navigable flow pattern of Hanqiao water fall project of the Yangtze River to the Huaihe River diversion project，analyze and evaluate the energy dissipation effect，and optimize the scheme according to the velocity distribution and flow characteristics of the original layout scheme. The results show that in the original layout of the Hanqiao water fall project，under the navigation conditions of 20-year return flow and 5-year return flow of the tributary，the transverse velocities at the confluence do not meet the requirements of the planning value，and the maximum transverse velocities are 0.46 m/s and 0.35 m/s. The energy dissipation effect of the optimized scheme is good. The transverse velocity and reflux velocity in the confluence area meet the design requirements. The maximum transverse velocities under adverse navigation conditions with a 5-year return period and a 20-year return period are 0.13 m/s and 0.25 m/s respectively. The optimized scheme can be used as the recommended scheme.