The methods of filling and leveling up and digitizing the main channel during the creating of the net of river based on DEM were discussed in the paper.The question of the incontinuity of the river caused by the low-lying can be resolved by using the method of filling and leveling up the low-lying.The question of the main channel may depart its natural position in the plat can be resolved through digitizing the main channel.Then,the net of river dealt by these methods is similar to the practical river net.Thereby the simulation results of hydrological elements will be more precise.