In this paper, the DEM (discrete element method) is used to simulate the gas-solid flow of a two-dimensional internally circulating fluidized bed. Eulerian and Lagrangian methods are used to deal with gas-field and discrete particles, respectively. The gas flow is determined by the local average Navier-Stokes equation, the motion of individual particle is obtained by solving Newton's second law of motion, and particle collisions are taken into account. The simulated results indicate that there is particle circulation from the high-velocity region to the low-velocity region in internally circulating fluidized beds with uneven air distributions; therefore, the mixing characteristics of the bed material are good. Through visualization experiments, we confirm that there is transverse movement of bubbles from the high-velocity side to the low-velocity side in internally circulating fluidized beds. Thus, particles in the trailing vortex of bubbles also move transversely. This is an important factor that results in particle circulation in internally circulating fluidized beds.