The Datengxia Water Conservancy Project has a large amount of construction with long period.It's necessary to take measures to guarantee the safety of channel navigation during the construction period of the hub.This paper establishes a physical model for the the layout plan of the first phase construction diversion cofferdam，and studies the water flow conditions and potential safety hazards of the open channel navigation under the engineering measures.The results show that the upstream head of the longitudinal cofferdam causes the slow flow area in the waist of the structure，and the open channel water body is narrow，which is not conducive to the navigation of ships during the construction period.After excavating the protruding part of the bottom of the main channel channel and adding a diversion structure at the front of the structure，the water flow in the open channel has been significantly improved.The velocity values of each measuring point are less than 5.00 m/s under the condition of maximum navigable flow rate.When the discharge flow rate is less than 12 000 m3/s，the velocity values of each measuring point are less than 3.00 m/s，which meets the requirements of self-navigation.The water surface along the diversion open channel with low gradient，and the maximum is -1.9‰.