This paper expounds the Changsha comprehensive hub stage II cofferdam closure plan, and puts forward the closure design scheme for the problems existing in the optimization schemes. Using the 1:100 fixed bed model, we research the scour from the water flow to the closure dike, the scour reach of the underwater riprap and the stability slope of the dike. The experiment shows that, we should choose the right closure position and width to reduce the scour of the dike kung; In addition, through the underwater site test, we obtain the scour reaches of different-sized particles and the stability slope of the dike, which lays a scientific basis for the construction organization design. The above conclusions have been used in the comprehensive hub in Changsha second phase construction of river closure cofferdam actual construction, and guaranteed the smooth completion of the closure project.