Abstract: Actually,for the flood routing,one of the most common hydraulic methods is the discrete method for the simplified form of the Saint-Venant equations. However,this method has some problems such as numerical instability and slow calculation speed. It is also a challenge for the description of fluid motion by the macroscopic method. The Lattice Boltzmann Method takes the distribution function as the research object. In solving nonlinear partial differential equations,there is a need for transforming it into the Lattice Boltzmann Evolution Equation which is a simple linear equation for solving the slow calculation speed of the macroscopic method. In this paper,the linear diffusion wave equation is used to describe the flood wave motion in the river channel. Instead of using the space coordinate,it adopts the multi-scale expansion method with five time scales to establish the D1Q5 model of Lattice Boltzmann Method for the linear diffusion wave equation and then to inquire into the inference of the flood process of downstream. The Muskingum Method,analytical solution method and the D1Q5 model of Lattice Boltzmann Method applied in flood computation at the Longjie-Qiaojia upper reaches of the Changjiang River and JiangnanFuxi downstream reaches of one hydropower station in Hunan Province. The simulation results of the flood peak relative error,peak appearance time and deterministic coefficient of the three methods are similar,which verifies the accuracy of Lattice Boltzmann Method. In addition,the influences of step length and relaxation time on calculation accuracy are also analyzed. The results show that the Lattice Boltzmann Method can effectively predict the flood process. And compared with the macroscopic method,the computational efficiency is greatly improved. The selection of space step value has a greater influence on calculation accuracy than the time step value. The appropriate space step should be selected,combined with the upstream and downstream section length. The value of the relaxation time is appropriate within the range of1.5,3.