Abstract: The coal washability is controlled by coal accumulating area.The research on relationship between characteristics of pyrite and clay mineral distribution and the coal genesis types of main minable coal seams No.9, No.10, No.12, No.13,and No.15,in the Wuda mining area,Inner Mongolia,indicated that the coal seams formed in a fluvial-dominated delta plain are characterized by low pyrite content,high clay mineral content and better washability,but the coal seams formed in tide-dominated delta plain are characterized by high sulfur,low clay mineral content and the mid degree of washability.In addition,the washability of pyrite and clay mineral of the coal seam formed in tidal flat is the worst.