Abstract: The characteristics of coal petrology and coal facies of the main minable coal seam No.9 areanalyzed. The washability of coal in different coal facies is discussed using the density distribution of coal samples from Wuda coal mining area, Inner Mongulia. The research results indicated that the washabilities of coal in same coal facies are similar, the sedimentary environment controlled the quantity and distrbution of minerals, and thus controlled the coal washability. The washability of coal deposited in high peat bogs is better than that deposited in low peat moors.