The gas-solid flow characteristics of the 35t/h oil shale-combustion circulating fluidized bed boiler (Developed by Wangqing Longteng Energy Development Co., Ltd) was simulated using Eulerian-Eulerian model (EEM), which was based on the kinetic theory of granular. The distribution of particle volume fraction and the distribution of particle velocity revealed the mechanism of the internal recirculation flow of particles in the furnace. The simulation results provided a reference for the flow structure optimization of the inner circulating fluidized bed and the enlargement of the inner circulating fluidized bed boiler.