The invention relates to a method for quantitatively characterizing the grain size of a main phase structure of a complex phase material, and belongs to the technical field of metal material physicalproperty inspection. By means of sample preparation, a section sample having microscopic difference between the main phase structure and a second-phase structure is prepared; EBSD surface scanning iscarried out, the calibration rate of the main phase structure is higher than 90%, the calibration rate of the second phase is lower than 10%, or even no diffraction pattern exists; finally, EBSD surface scanning data analysis is carried out to remove false points, singular points and noise points in a scanning result, then the calibrated data points of a second phase are set as a zero solution through a small particle removing mode, or a lining degree range corresponding to the second phase in a diffraction contrast graph is set as a zero solution, the noise point removal process is repeated,and grains of the main phase structure are quantitatively analyzed. The method has the advantages that the microscopic morphology of the main phase grains of the complex phase material can be clearlyand visually displayed, and quantitative characterizing is conducted on the grain size.