Abstract: In this paper, bottom ash (BA), fly ash (FA) and feeding pulverized coal (FPC) are sampled from an operating power plant of China National Energy Group in Jiangsu. They are separated into density fractions between 1.3~2.5g/cm³ using a float-sink method. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction(XRD) and X-ray fluorescence(XRF) are used to analyze their morphology and chemical composition. FactSage7.3 is adopted to calculate their liquid content between 900~1500℃. The chemical composition and particle size distribution of FPC are used to calculate the yield and source of BA and FA. The results indicate that BA consists of density fractions between 1.3~2.0g/cm³. The carbon content deceases with increasing density, coinciding well with the liquid trend. FA mainly consists of density fractions between 1.8~2.5g/cm³, in which the > 2.5g/cm³ fraction accounts for 48.42%. No clear relationship exists between the carbon content, density, and liquid content. FPC is distributed between 1.3~2.0g/cm³ in density. Under 1300^oC, the liquid content of density fractions decreases with increasing density. > 1.8g/cm³ fraction has the lowest liquid content, attaining 36%. Under 1500℃, the lowest liquid content is 56%. Theoretical analysis and quantitative calculation both show the formation mechanism of bottom ash. With the burnout of coal chars, ash particles with a large size and high liquid content will collide, adhere and agglomerate due to the strong mixing action in the coal-fired power plant furnace, forming BA. Ash particles with a small size and low liquid content will flow with the flue gas and cool down to form FA.