The navigable flow condition of the entrance area and connecting section of the approach channel in muti-line ship locks is a key research topic.Taking the navigation hydraulics test of the second-line lock of Guding water conservancy hub as an example,this paper studies the navigable flow conditions in the entrance and connecting section of the lower approach channel under the background of the construction of Guding second-line lock.The test results show that the velocity of reflux and cross flow in the entrance and connecting section exceeds related standard.Therefore,from the two aspects of layout of navigation wall and dredging approach channel connection section,this paper puts forward a variety of optimal layout schemes,and recommends the combination of layout of 70 m external cantilever navigation wall (50 m vertical wall+20 m external cantilever) and dredging connection section to improve navigable environment.The research results provide a reference for the optimal layout of the second line lock of the Guding hydropower station.