Abstract: To ensure the good fluidization and sufficient combustion in large CFB boilers, the control over the coal particle size distribution is quite strict. Through the analysis on the issues in the screening system operation of a 300-MW CFB boiler, the optimized design of the two-stage crushing and the three-stage screening is put forward and applied to a 600-MW CFB boiler. The practical operation proves that, based on the design optimization and good maintenance of the crushing and screening system, the coal particle sizes can meet the boiler operation requirements.