Bank collapse caused by scouring occurs frequently in the middle and lower reaches of the Yangtze River and leads to huge damages.In order to search the mechanism of bank collapse happening in the straight river section,we carry out the observation and analysis by means of simulation experiment.There are five main kinds of currents with different movement characteristics in the process of bank collapse.Crescent sand waves，lying near the surface of water，are important transport carriers for sediments and may lead to sustained and formative of bank collapse.The aboved opinions are approved by slope protection simulation experiment.Comparing to protecting the toe area,protecting the area near the surface of water is more conducive to effectively controlling bank collapse from the engineering point of view.Meanwhile,reasonable protection of toe area is necessary to avoid continuous erosion of unfavorable influence to slopes in the future.