The navigation-power junction artificial regulation will cause the change of water level and velocity in the downstream channel,and affect the the condition of navigation.Based on the the typical mountainous waterway,Lanjiang under the navigation-power junction regulation,a numerical model is established to study the hydraulic characteristics of water level and velocity change under different return periods after the completion of Yaojia hub and Lingma hub,and the designed highest navigable water level is obtained from the simulation.The results show that:The characteristic water level under the flood of once 10 years and once 5 years is much bigger than the warning water level,and the velocity of partial area is large under the case of the flood of once 3 years;These go against the safety of navigation;Combining the construction of waterway and economic benefits and the safety of running,and according to the control velocity obtained by the synthetic duration curve method,the water level under the case of 90% flood frequency should be considered as the designed highest navigable water level.