Located in the upstream of the Yuanjiang River, Dafutan navigation-hydropower project is in mountainous restrictive channel with complex flow condition unfavorable for navigation. The entrance and connection segments of the upstream and downstream approach channels are featured with unfavorable flow condition, large transverse flow velocity, and insufficient water depth for navigation under low flow. In view of this, we designed and constructed a physical model of the shiplock of Dafutan project to comprehensively investigate the navigation flow condition in the entrance and connection segment of approach channel and the sandbar tail. Ship model test demonstrated that the original layout of the project and the navigation structures are unreasonable. The navigable flow condition of the entrance and connection segment of upstream lock approach channel is subjected to the cross current at the middle sandbar under the circumstance of simultaneous discharge of left and right branches, difficult for ship navigation. In order to improve the flow condition, we take measures such as elongating the navigation wall, building spur dike and longitudinal dike along the bar tail, and excavating the navigation channel. We found that the navigation condition and the flow condition of ship model had obviously improved under the optimized layout scheme 4. In addition, we determined the maximum navigable discharge under the optimized scheme 4, and demonstrated the safety and engineering feasibility of the optimization.