Qujiang channel (Jinhua section) is located on the upstream of the Qiantang River，and Yaojia junction is the most downstream cascade project of Qujiang (Jinhua section) shipping cascade development projects.The dam site was moved up in order to reduce the tributary immersion，with the consequences that the backwater of Fuchun river dam could not connect with the downstream water level of Yaojia junction.So，about 7 km downstream channel needs to be excavated deeply to meet the requirements of navigation.To maintain the stability of artificially excavated channel in the mountainous river，we set appropriate height of sand retaining sill to stop the river sand into deeply excavated channel.Based on the fixed bed and moving bed physical model test，we analyze the flow condition，bed changing，as well as the effect of sand retaining sill of the downstream channel of navigation lock，and demonstrates the design schemes of deep excavation of channel and sand retaining sill to provide reference for decreasing the channel maintenance volume and ensuring the clear waterway of the downstream channel.