Abstract: In order to understand the composition characteristics of circulating fluidized bed (CFB) boiler pulverized fuel ash, the fly ash and bottom slag of CFB units from four typical power plants in Pingshuo, Hepo, Hongguang and Guofeng of Shanxi Province were collected. The chemical and phase compositions of ash with different particle sizes were studied. The results show that the particle size distribution of CFB pulverized fuel ash from different power plants has some similarities. More than 75% of fly ash distributed between 96～109 μm(140～160 mesh)and 61～80 μm(180～240 mesh). Compared with fly ash, the distribution of bottom slag is relatively dispersed, and the proportion of each particle size range is below 25%. From the perspective of the particle size screening effect, bottom slag is easier to sort than fly ash. The chemical composition of fly ash varies little with particle size. The chemical composition of bottom slag is more pronounced with particle size. The contents of SiO2 and Al2O3 in the bottom slag decrease with decreasing particle size, and the contents of CaO and SO3 increase with decreasing particle size. The content of Fe2O3 and MgO does not change with particle size. After sieving, there is no significant difference in mineral species between fly ash of different particle sizes. Quartz, anhydrite and hematite are the main components; quartz, anhydrite, calcium oxide and hematite are the main components in slag, and anhydrite content increased with decreasing particle size,which indicating that the sulfur-fixed product is more easily distributed in small particle size bottom slag.