If the fuel particle size is too big, it will easily accumulate at bottom of the boiler, increasing the incomplete combustion of fuel and causing the decreasing of combustion efficiency. The longer time passes, the more the big particle size will accumulate, and the poor fluidization will be caused and the local of combustion chamber will coke. In the mean time, the too big fuel particle size will cause insufficient circulating ash and less combustion share in dilute-phase zone, so that the boiler output will be decreased. The too small fuel particle size will easily cause the bed of material layers to become thin or empty by blowing, thus it is difficult to from stable dense-phase zone. Although the combustion efficiency has been improved to some extent, the burden of return feeder is increased and the return feeder is easily blocked by ash or easily cokes, therefore the reasonably proportioning of the fuel particle size is the necessary condition for ensuring the normally fluidizing and burning of boiler. During operation, the bed temperature shall be specially highlighted. If the bed temperature is too high，the materials will easily coke; if the bed temperature is too low, fire will easily go out and the combustion efficiency will be reduced. Generally the temperature is controlled to be 850℃—900℃, it shall not be lower than 800℃. When there is higher load, the bed temperature may be properly increased, the maximum shall not exceed 950℃. When the bed temperature changes greatly and the coal-feeding cannot meet the adjustment requirement, the method of increasing or decreasing primary air can be used for strengthening the control to the bed temperature, in order to prevent the occurrence of combustion accident.