In order to change the particle size of TiO₂ and improve photocatalytic performance, TiO₂ powder was treated by high-energy ball milling. The effects of ball milling time on the morphology, crystal structure, Raman spectrum, fluorescence spectrum and Photocatalytic Performance of the samples were studied; The relationship between fluorescence spectrum and photocatalytic performance was analyzed to identify the photocatalytic mechanism and provide a basis for quickly judging the photocatalytic performance of photocatalysts. The results showed that with the increase in milling time, the sample particles changed from regular to irregular shape, and the surface became rough. All samples were mainly anatase structures with a small amount of rutile structure. With the increase of ball milling time, the (110) diffraction peak of rutile structure gradually increased, indicating that a small amount of TiO₂ had undergone phase transformation during ball milling, and the grain size first decreased and then increased. All samples showed the Raman scattering peak of anatase TiO₂, but the Raman scattering peak of rutile crystal was not found. The FWHM of each Raman peak increased with milling time, indicating that the sample's surface quality decreased, and the surface defects and oxygen vacancies gradually increased. All samples hada fluorescence peak near 470 nm, and the fluorescence peak of the samples after ball milling was enhanced. The TiO₂ samples after ball milling had fluorescence peaks at 397, 452, 483, 500 and 536 nm, and the intensity of TiO₂ fluorescence peaks after ball milling for 4 h was the strongest, indicating that the surface defects and oxygen vacancy content were the most, which was consistent with the results of Raman spectroscopy. With the increase of irradiation time to 100 min, the degradation rate of all samples increased, and the degradation rate of methyl orange exceeded 60% after 100 min. The degradation rate of TiO₂ samples after ball milling was higher than that without ball milling, and the degradation rate of samples milled for 4 hours was the highest, indicating that its photocatalytic performance was the best. In the photocatalytic reaction process, oxygen vacancies and defects became the center of capturing photogenerated electrons, so the recombination of photogenerated electrons and holes was effectively prohibited. The oxygen vacancy in the sample contributed to the absorption of oxygen. Oxygen interacted with photogenerated electrons captured by oxygen vacancies to form oxygen radicals, which played a key role in the oxidation of organic compounds. Therefore, the more oxygen vacancies and surface defects, the stronger the exciton photoluminescence peak, the better its photocatalytic performance. The photocatalytic performance of TiO₂ powder can be improved by ball milling, and photocatalytic performance can be judged quickly and qualitatively by the intensity of exciton photoluminescence peak.