Nano-TiO_2particles was prepared by sol-gel method. A lot of factors that affect the photocatalytic activity of nano-TiO_2were studied by the degradation of methyl orange. The obtained TiO_2are characterized by TEM, XRD,etc. Results show that TiO_2shows optimal photocatalytic activity when the volume ratio of TNB, ethanol, acetic acid and distilled water is 10∶19∶8∶4, baked at 500℃ for 2hours, and the proper dosage of TiO_2is 1g/L; the as-prepared TiO_2is anatase phase, and the mean size is 10～20nm.