High energy ball milling method was a common method in the process of material preparation, which produced crystal vacancy defects through the material running with high speed to achieve the doping of elements, so the chemical adsorption or chemical reaction has occurred. New phase formed, and it has a great impact on the performance of subsequent synthetic materials. Barium ferrite has been used in many functional materials because of its good magnetic properties. In the paper, barium ferrite precursor was prepared by the high energy ball mill method. Using XRD, SEM and FTIR methods, the changes in phase, microstructure and functional groups of barium ferrite precursor with different high energy ball milling times were investigated. By the second derivative infrared spectroscopy and smooth fitting calculation method, the phase changes were quantitatively analyzed in the process of high-energy ball mill of materiel. XRD and SEM results show that with the increase of ball milling time, the diffraction peak width of each phase of the barium ferrite precursor becomes wider, the powder is refined, the crystal lattice is gradually distorted, and crystal vacancy defects are produced, so that Ba dissolves into the Fe₂O₃ lattice to produce the solid solution of Ba_xFe_2-xO₃, and the adsorption “agglomeration” is produced phenomenon. When the milling time was longer than 40 h, the “nano-size effect” occurred, and magnetic Fe₃O₄ and Ba_xFe_3-xO₄ solid solutions were generated. The results of infrared spectrum analysis showed that the characteristic peaks of BaCO₃ and α-Fe₂O₃ decreased and shifted significantly with the increase of ball milling time, indicating that the particle size of decreased and chemical reactions occurred with the increase of ball milling time. The smooth fitting spectrum and the second derivative spectrum of the infrared spectrum showed that the area of each absorption peak decreased obviously with the increase of the milling time. Compared with that of ball milling under 0h, after ball milling for 10, 20 and 40 h, the vibration absorption peak area of Fe—O bond at 473 cm^-1 decreased by 48.84%, 65.97% and 93.54%, respectively, and at 540 cm^-1, the absorption peak area of the Fe—O bond decreased by 37.11%, 51.76% and 82.85%, respectively. Similarly, the absorption peak area of in-plane bending vibration of the O—C—O bond at 856 cm^-1 was 30.62%, 44.71% and 67.10%, respectively, and the peak area of C—O bond asymmetric stretching vibration at the wavenumber of 1 446 cm^-1 decreased by 0.03%, 27.63% and 57.90%, respectively, compared with that of ball milling at 0 h. In this way, the phase changes of barium ferrite precursors during high energy ball milling were investigated, and the percentage changes of reaction product content were accurately determined based on quantitative analysis, which has important guiding significance for the research on the changes in subsequent materials synthesis and properties with the phase changes of barium ferrite precursor.