In order to quantitatively characterize the twophase or multiphase structure in steel, the BS values in field emission scanning electron microscopy (FESEM) and electron backscatter diffraction (EBSD) were applied in the detailed study and discussed. The experimental results showed that for the singlephase ferrite, bainite or martensite, the BS gray distribution map showed an approximately normal distribution, and the BS map can present an image similar to the structure. Using the BS value, the phase separation of the twophase or multiphase structure with similar structure can be well quantified. In the case of phase separation quantification, the appropriate fitting function needs to be selected, thus the quantitative result can be more accurate.