The Longxikou navigation-power junction on Min river is a comprehensive hydro-junction of navigation combining with hydropower. Because of the importance to Min river navigation, the flow condition during the construction period of Longxikou power station will be directly concerned if Min river navigation channel can meet the transport requirements of the large ship or not. Based on the hydraulic model test, the navigation water condition in each construction period is studied. In some cofferdam sections of the second and the third period of diversion, the condition of navigation flow is very poor. To solve these problems, some comprehensive measures,which improve the navigation flow conditions in the construction period, are proposed. The research result may serve as reference for similar engineering.