The study of optimizing the shape of the diversion channels is crucial for saving project investment and ensuring construction safety.This paper applies a two-dimensional water flow mathematical model to study the effects of the incoming flow conditions and the optimization methods for the the shape of diversion channels on the overflow capacity of the diversion channels and the hydraulic characteristics of engineering reach.The results show that when the cross-sectional area of the same size diversion channel is expanded,compared to increasing the width of the channel bottom,the height of backwater in the upper reaches of the diversion channel is lower and the turbulence in the internal and outlet of the diversion channel is weaker.With the increase of the section area,the difference of the maximum relative backwater height in the upper reaches of the diversion channel between the two schemes increases.The maximum relative backwater height increases with the increase of flow rate.In the scheme of increasing channel depth,the maximum flow velocity inside the diversion channel is smaller,and the flow return state is better,and the flow velocity and backflow strength are smaller.