Abstract: In order to better comprehend the fate of coumoxystrobin in the environment, the photolysis of coumoxystrobin under different light sources (500 W xenon lamp and 20 W mercury lamp), initial concentrations (1, 5, 10, and 15 mg/L) and pH values (4, 7 and 9) were investigated based on the method recommended by China Test Guidelines on Chemical Pesticide Environmental Safety Assessment via high-performance liquid chromatography. The results demonstrated that the photolysis of coumoxystrobin under the experimental conditions matched quasi first-order kinetic equation. The photolysis half-lives under 500 W xenon lamp and 20 W mercury lamp were 2.23 and 1.10 h, respectively. The photolysis rate of 20 W mercury lamp was about twice that of 500 W xenon lamp. Under the same irradiation conditions, the photolysis rate decreased with the increasing initial concentrations, which were negatively correlated. The photolysis rate of coumoxystrobin in the three buffer solutions showed as follows: pH 9 > pH 4 > pH 7. Tween 80 could inhibit the photolysis of coumoxystrobin. The study provide references for the rational use and environmental assessment of coumoxystrobin.