Abstract: The kaolinite in coal strata was grinded in mill for 0～2 h,and then be heated at the temperature of 900℃,1000℃,1400℃ for 1 h respectively.Also the instrument of XRD,DTA,IR were used to research the crystal structure and thermal behavior of kaolinite after being grinded.The results show that after 1 h of grinding,the crystalline order of kaolinite is destroyed.Grinding for 1 h produce a favorable state for forming mullite-type crystals after beating even at 1000℃.