Abstract: To analyze the movement mechanism of particles in a fluidized bed under different intake modes from micro perspectives, numerical simulations were conducted on the motion state in the fluidized bed using computational fluid dynamics and discrete element method, while the Gidaspow drag force model was adopted to achieve the coupling of gas-solid two phases. The mixing state of the particles was qualitatively and quantitatively analyzed by the Lacey mixing index, and the influence of velocity parameters on the mixing characteristics was discussed. Results show that the particle mixing effectiveness in the spouted fluidized bed is affected by the velocity of both the spout and background gas; the final mixing state with spout gas is better than that with uniform gas intake; introducing the background gas in the presence of spout gas will make the dead zone become smaller, and the larger the background gas velocity is, the smaller the dead zone will be. In particular simulation conditions, there exists an optimal background gas velocity, when the particles are mixed most adequately in the bed.