Aiming at the characteristics of bubbling and sieving of coal in fluidized bed type sieving machine,based on a Eulerian multiphase flow model,the gas-solid flow of single particle size in sieving machine was studied by numerical simulation.The solid phase volume share distribution on a cross section and the distribution of bubbles on different cross sections in sieving machine were acquired.In order to identify the optimum fluidization velocity,four working conditions with different inlet gas velocity were designed.According to the simulation results of the four groups,the optimum fluidization velocity(u=0.96 m/s) was concluded.By comparing the fluidization effect of the four groups,it is found the number of bubbles is the largest when fluidization velocity is 1.36 m/s,so this working condition is the most representative to study the bubbling characteristics.The results show that the bubble in sieving machine is of randomness and nonuniformity.