The granulation of blast furnace slag (BFS) with water quenching treatment has some disadvantages, such as high water consumption and difficulty for recovery heat. So developing a new dry granulation technique to treat BFS is very important. The applicability of BFS directly depends on the content of non-crystalline solids in the slag after treatment. So it is of theoretical and practical significance to analyze the content of non-crystalline solids in the slag quantitatively and simply. Metallographical test is mainly adopted to quantify the non-crystalline in BFS so far with the shortages such as complex sample, difficult determination, ect. The diffraction intensity of non-crystalline is proportionate to the content of non-crystalline in BFS, X-ray diffraction method was adopted to quantify the noncrystalline and the crystalline solids in BFS. The quantitative coefficient between the crystalline and the non-crystalline solids of BFS is 0.70 of BFS whose main composition (mass percent, %) is: CaO 38. 2, SiO2 35. 7, Al2O3 16. 3, and MgO 8. 3. The relative error of X-ray diffractometer for quantitatively analyzing non-crystalline content of BFS is less than 1%.