Based on RNG k-ε two equations turbulence mathematical model of VOF method，the hydraulic characteristics and downstream navigable flow pattern of the Wulaoyan water drop project of the Yangtze River to the Huaihe River diversion project are numerically simulated 3D，the transverse velocity and flow pattern characteristics of the navigable area at the confluence are studied，and the reasons why the navigable flow conditions at the confluence in the original design scheme do not meet the specification requirements are analyzed. The original design scheme is adjusted and optimized by measures such as retreating through water drop project，reducing the confluence angle and optimizing the connection radian between wing wall and main canal. The results show that the transverse flow velocity and return flow velocity in the confluence area of the optimized engineering scheme meet the design requirements. The maximum reflux velocities under the 5-year and 20-year navigation conditions are 0.10 m/s and 0.16 m/s respectively，and the maximum transverse velocities are 0.13 m/s and 0.27 m/s respectively，which can be used as the recommended scheme.