Abstract: A quantitative proton nuclear magnetic resonance spectroscopy (¹H-qNMR) method was established to investigate the photocatalytic degradation mechanism of phenol using UV/TiO₂, with dimethyl sulfoxide (DMSO) as the internal standard reference. The intermediate compounds of phenol during the photocatalysis process were identified, and quantification analysis was performed using specific signals at 8.26, 7.22, 6.76, 6.71, 6.23, 3.25, 3.18, 1,96, 1.08, and 2.62 ppm for formic acid, phenol, bis(4-hydroxyphenyl) ether, hydroquinone, maleic acid, methanol, malonic acid, acetic acid, and ethanol, respectively. The ¹H-qNMR method revealed that the photodegradation of phenol in UV/TiO₂ specifically begins with the hydroxylation of the para-hydrogen of phenol, leading to the subsequent formation of the dimer bis (4-hydroxyphenyl) ether, which has not been previously mentioned in the existing studies. The ¹H-qNMR method offers innovative ideas and tools for confirming photocatalytic degradation pathways and uncovering catalytic mechanisms, making it a valuable tool for evaluating the photocatalytic degradation activity of catalysts.