Abstract: Firstly the phases in blast furnace slag were determined by chemical analysis and X-ray diffraction analysis. And then the content of each phase was quantitatively analyzed by adding standard materials CaF2 and the amorphous content was also calculated by K-value method. The results indicate that the amorphous phase content in blast furnace slag can be quickly and accurately determined by combining X-ray diffraction method and K-value method, and when the standard materials CaF2 addition amount is 20%, more accurate results can be obtained.