The navigation scale of mountain canal is small,with large gradient,fast flow velocity,obvious changes in dry and wet seasons,and complex hydrological conditions.The reconstruction project of Lishui Liandu Bihu Bridge is located in the middle reaches of the Oujiang River mainstream.The current and planned canal routes of the river section it crosses are different,and the bridge construction needs to meet both the requirements of current canal navigation and reserved planned canal development space.Therefore,higher requirements are put forward for the layout of bridge piers.Through calculation and analysis of the navigation clearance scale of the bridge,it is shown that the planned canal layout meets the navigation requirements within the main span of the main bridge,while the current canal layout is within the left span of the main bridge,and the left main pier is located at the edge of the current canal,which will have an impact on the navigation safety of the current ship.Using a planar two-dimensional flow and sediment mathematical model,the impact of bridge reconstruction on the current and planned canal flow conditions and sediment erosion and deposition is studied.Improvement measures are proposed to widen the current canal to the left by 4 meters to meet navigation requirements,which can provide reference for bridge reconstruction projects across mountainous areas.