Abstract: Based on the field data,the lateral erosion in the downstream of the resemvir is dealt with in the paper.The effect of lateral boundary condition,the river regime and the bed material on lateral erosion are analyzed.Some conclusions could be drawn:①The lateral erosion does exist in the downstream of the resemvir.The lateral erosion is slight at the begining,and then gradually enhanced,sometimes the lateral erosion in the downstream may result in a bigger width than before;②In the reaches where the lateral boundary conditions are strong,the lateral erosion is weak and it is strong in the reaches where the lateral boundary conditions are weak;③In the reaches where the bed material is coarse and the material in the bank is fine,the lateral erosion is strong,while in the reaches where the bed material is fine and the erosive resistance of bank is strong,the lateral erosion i s weak;And④in the bifurcated reaches,the lateral erosion mainly happens in the main channel;In the wandering reaches,the character of wandering is controlled firstly and the effect of lateral erosion is submerged;In the meandering reaches,the phenomena of the cut-bank and thrown-away-elbow are prevalent.