This paper analyzes the main types and factors of bank collapse under the effect on water erosion and corrosion ,forecasts the main way of destruction, calculates and analyzes the width of 20 sections of the bank by using the Graph method and Kachugin method respectively.The results show that the width of bank collapse was calculated by using Kachugin method has a great difference with reality, however, the results by graph method conforms with reality. So it can be flexibly analyzed and applied for practice engineering.