The cantilever failure is one of the typical bank failures,in which the lateral caving erosion at the bottom of the bank plays an important role.When the caving erosion width is larger than a certain value,the cantilever failures such as shear,toppling and stress failures may occur.In order to understand the condition of the cantilever failure,the collapse mechanisms of the cantilever failures are studied based on the bank stability theory and flume experiment.According to the bank stability equation with the lateral erosion,the critical caving erosion width(CCEW) formulas for the shear and toppling failures of simple slope bank were derived in this paper.The formulas show that the CCEW increases as the overhanging soil thickness and soil cohesion increase,and decreases as the crack depth on the bank surface and the slope angle of the bank increase.And these formulas were tested with experimental data,which shows the predicted values are good agreement with experimental data.The paper reveals a quantitative expression on the process of the river cantilever failure. The cantilever failure is one of the typical bank failures, in which the lateral caving erosion at the bottom of the bank plays an important role .When the caving erosion width is larger than a certain value, the cantilever failures such as shear, toppling and stress failures may occur. order may understand the condition of the cantilever failure, the collapse mechanisms of the cantilever failures are the cantilever failures are the bank stability theory and flume experiment. According to the bank stability equation with the lateral erosion, the critical caving erosion width (CCEW) formulas for the shear and toppling failures of simple slope bank were derived in this paper. The formulas show that the CCEW increases as the overhanging soil thickness and soil cohesion increase, and decreases as the crack depth on the bank surface and the slope angle of the bank increase. These formulas were tested with experimental data, which shows the predicted values ​​are good agreement with experimental data. The paper reveals a quantitative expression on the process of the river cantilever failure.