In view of the problem that the actual maximum navigable flow after the construction of the navigation and power junction in mountainous rivers can’t meet the requirement of the code，we study the maximum navigable flow after the arrangement of the navigation and power junction in mountainous rivers. Based on the Dongfengyan navigation power junction，we analyze the flow and navigation conditions of the entrance area and the connecting section of the upper and lower approach channels of the ship lock by means of physical model test and ship model test，and put forward suggestions on the maximum navigation flow for safe navigation of Dongfengyan navigation power junction，and come to the conclusion that the maximum navigable flow of the medium-low-head hydro junction in the mountainous river should not be lower than the forbidden flow of the natural river. The research results may serve as a reference in the determination of the maximum navigable flow of the middle-low-head hydro junction in mountainous rivers.