Abstract: Based on kinetic theory of granular flow, numerical simulation was conducted on the gas-solid two-phase flow in dense-phase zone of a high-low circulating fluidized bed boiler using Euler-Eluer two-fluid model and standard k-ε model in Fluent software, so as to analyze the variation law of flow velocity and pressure distribution of particles in the internal circulation process, and to study the effects of bed velocity on the flow characteristics in dense-phase zone. Results show that at the secondary bed velocity u2=1.5 m/s, the time-averaged volume fraction of particles reduces in primary bed and increases in secondary bed, while both the standard deviation of pressure drop and reflux velocity of particles increase, with the rise of primary bed velocity; whereas, at the primary bed velocity u1=4.0 m/s, with the rise of secondary bed velocity, the reflux velocity of particles reduces, and the standard deviation of pressure drop increases first and decreases later on, which reaches the maximum in the case of u2=2.0 m/s.