Abstract: The photodegradation kinetics of acetochlor in water was studied under the treatment of the illumination of high-pressure mercury lamp and sunlight by the different wavelength filter. The photo -degradation kinetics of acetochlor accorded with the first order kinetic equation at the presence of Humic acid,the photodegradation rates of acetochlor slowed down as wavelength extending,the photodegradation halflife of acetochlor prolonged.The marked diversity was observed as compared with no filter treatment.It indicated that the photodegradation of acetochlor in water was significantly related to light wavelength.