The invention belongs to the technical field of cotton fabric finishing, and relates to a photocatalytic self-cleaning functional cotton fabric and a preparation method thereof. The preparation method provided by the invention comprises the following steps of dissolving ammonium molybdate tetrahydrate and copper nitrate in an organic solvent, stirring until the ammonium molybdate tetrahydrate and the copper nitrate are dissolved, then adding 1, 2, 4-triazole, carrying out ultrasonic treatment to dissolve the 1, 2, 4-triazole, and adjusting the pH value to 2.5-8.5 to obtain a treatment solution; soaking a washed cotton fabric into a sodium chloroacetate solution, reacting for 5-20 minutes at room temperature, taking out, washing and drying to obtain a cotton fabric subjected to etherification modification treatment; and putting the cotton fabric subjected to etherification modification treatment into the treatment solution, conducting ultrasonic treatment for 3-8 h, conducting stirring for 12-24 h at the room temperature, then taking out the cotton fabric, washing and drying, and obtaining the photocatalytic self-cleaning functional cotton fabric. The photocatalytic self-cleaning functional cotton fabric prepared by the preparation method disclosed by the invention is stronger in light absorption capacity, more in photocatalytic reaction sites and more excellent in photocatalytic self-cleaning performance.