To control material circulation is the difference of the operation of circulating fluidized bed boiler operation with that of the conventional boiler. According to the characteristics of combustion and heat transfer of circulating fluidized bed boiler, the material circulation plays a pivotal role for the operation of the circulating fluidized bed boiler, because it can make uniform temperature field distribution at upper part of the boiler hearth (combustion chamber), exchange heat with water cooled wall through a variety of heat transferring mode, therefore it has higher heat transfer coefficient. Adjusting the circulation quantity of material can control the bed temperature and differential pressure in hearth, and further adjust the boiler load. The material circulation increasing can make the temperature of the  whole combustion chamber tend to be more uniform and can increase the retention period of fuel in the boiler,  thus improving the combustion efficiency. The circulating materials level has a direct relationship with the separation efficiency of boiler. The higher the separation efficiency of separator has, the bigger returns separated from the flue gas has,  thus the surplus adjusting the load by the boiler will be bigger, which will be helpful to improve the utilization efficiency of the boiler  and the utilization efficiency of CaO, reduce the Ca/S ratio, and improve the desulphurization efficiency.    (lsh)