Beach body is an important part of the river channel，which plays an important role in stabilizing dry channel and controlling waterway pattern.Therefore,it is particularly important to protect and control the beach during the course of waterway regulation.Based on the middle reaches of the Yangtze River channel,through the generalized model test of the unsteady flow,the acceleration of water flow at different positions on the side beach body was observed,the force on the side beach and the reason for erosion were analyzed,and the transverse and longitudinal distribution law of water flow on the side beach and the change characteristics of the side beach easy to be scour were obtained.The research results have certain theoretical guiding value for the regulation of the side beach guarding project in the middle reaches of the Yangtze River.