In order to improve the computation accuracy of the Muskingum flood routing model, a new method of parameter estimation for Muskingum model based on the improved grey wolf optimizer (IGWO) is proposed and applied to the flood calculation in the south canal between Chenggouwan and Linqing River. The experimental results show that IGWO can effectively estimate the parameters of the Muskingum model. Compared with the other parameter estimation methods of Muskingum routing model, IGWO has higher calculation accuracy and better optimization performance.