Abstract: Aiming at the problems of selection and separation basis in the intelligent separation process of coal and gangue,the change rule of gray value of mineral and coal with different nature at different scales and densities was studied by X-rays identify minerals principle and image grayscale extraction method. The results show that the grayscale value of single mineral and mixed mineral decreases gradually with the increase of thickness and density. At the same thickness,the higher mineral density is,the smaller the gray value is,and this result is also applicable to different coal type. The regression equation for single mineral and mixed mineral was obtained by regression analysis method. The regression equation coefficients a of graphite,quartz,kaolin and montmorillonite in high and low energy regions are 59.25,65.69,61.61,58.02 and 174.95,177.31,186.95,161.81,respectively. Graphite is mixed with other three minerals to produce graphite ∶quartz,graphite:kaolin,graphite:montmorillonite,graphite:kaolin:quartz,graphite: montmorillonite:kaolin,graphite:quartz,graphite:montmorillonite:kaolin,and the regression equation coefficients in high and low energy regions are 151.12,156.00,153. 13,152.43,152.98,151.98 and 193.34,201.34,192.93,191.26,194.68,193.08,respectively. Then,the regression equation of single mineral was used to verify the mixed minerals. It is found that the gray-scale interval corresponds to the density interval,which conforms to the principle of X-ray recognition. The gray-scale values of different kinds of coal( coking coal,fat coal,gas coal) have a highly significant regularity with their thickness and density,and the change trend was consistent with that of single mineral and mixed mineral.