Minjiang hydropower station dam water treatment project is the low dam without gate.So it can not control the flood and regulate location of discharge.Whether the level of the upstream flow is large or not,it will bring great impact to the navigation conditions of downstream approach channel .Based on the features of water movement and siltation problems,utilize principles of hydraulics and sediment movement theory,create some technical methods such as isolating water and cutting off path of sediment flow.By subjoining cut-off wall and sediment sill as well as optimizing the layout of dolphins,the flow conditions within the approach channel are changed better and also effectively prevent silting.Model test results show that the navigable index such as depth and flow rate in approach channel all can meet the regulatory requirements.The methods which presented in this paper can provide a reference for similar projects.