Abstract: Alumina and aluminium hydroxide have many crystal types.The uses are quite different between different crystal types of alumina and aluminium hydroxide.Therefore，it is very necessary to identify their crystal types.XRD has its unique advantages in the field of appraising matter′s crystal type.Based on the predecessor′s work，X-ray diffraction patterns and characteristic diffraction peaks of alumina and aluminium hydroxide with different crystal types were introduced.The difference and appraising method of diffraction peaks were analyzed.In addition，the uses of alumina and aluminium hydroxide with different crystal types were briefly introduced.