Abstract: The inevitable result of circulating fluidized bed( CFB) boilers scale-up is the increasing of furnace cross-sectional size and the parallel circuit. The coal combustion and heat transfer in a fluidized bed boiler are determined by the characteristics of gas-solid flow in the furnace. The uniformity of gas-solid flow has an important impact on the safe operation of CFB boiler. In this paper,the static and dynamic lateral non-uniformity of gas-solid flow in large CFB boilers were analyzed. The static non-uniformity problems include the air distribution uniformity,the gas-solid flow deviation along the section caused by the parallel circuit and the flow distribution deviation of each circuit,which does not change with time under the stable operation condition. The resistance characteristic of separator is an important characteristic parameter of cyclone. Under the same gas phase flow rate,the effect of solid concentration on the pressure drop of cyclone is non-monotonic. The cyclone pressure drop decreases first and then slowly increases as the concentration of solid particles increasing. The solutions of the governing equation of multi-cyclone system are multi-velued. Therefore,the solid circulating rate of each cyclone has deviation under the condition of multi loop parallel. The hanging platen superheater in CFB boiler affects the local concentration distribution of particles and then affects the distribution of solid particle circulation flow rate of each separator. In the aspect of air distribution uniformity,the way of air inlet from both sides and the back wall will lead to uneven air distribution in different degrees. The outlet duct of the cyclones has a significant influence on gas-solid flow distribution of the cyclones. The large margin and long-term pressure fluctuation in CFB furnace is discovered during lower load operation,which is the dynamic lateral non-uniformity. The large cross-section air distribution,reduction of the primary air and the multi-circuit parallel are main reasons for this problem. The mathematical model of lateral fluctuation is based on the assumption of natural frequency of lateral fluctuation of gas-solid two-phase flow system. When the disturbance frequency is close to natural frequency,lateral wave will be generated. The dynamic non-uniformity problem is lack of in-depth and systematic research on the laboratory scale,and the mechanism is still relatively vague,which is the main research direction of the gas-solid flow non-uniformity problem. At the same time,the coupling effect of uneven wind distribution and dense phase gas-solid flow needs further study.