Abstract: The photochemical degradation of azoxystrobin in several organic solvents and water plus their relevant effect factors were studied under the irradiation of Xenon lamp with 500 W. The results showed that the half-life of azoxystrobin in aqueous medium was 5.8 hours at the concentration of 5 mg/L. The photolytic rate became slower with increasing concentration of azoxystrobin in water at 2 to 20 mg/L. The photolytic rates of azoxystrobin in different media showed the following sequence: acetonitrile >water >methanol >n-hexane >acetone, the half-lives were 4.8, 5.8, 11.5, 12.1 and 23.5 h, respectively. In aqueous solutions,nitrate showed photosensitizing effect on the photo-degradation of azoxystrobin. At the NO3concentrations of 1, 2, 10 and 20 mg/L, the half-lives were 5.5, 5.1, 4.5 and 3.9 h, respectively. The NO2 showed photosensitizing effect on the photo-degradation of azoxystrobin at the concentrations of 1 to 2 mg/L, but it showed photo-quenching effect at the concentrations of 10 to 20 mg/L. The presence of Fe and surfactant of sodium dodecyl sulfate (SDS) showed photosensitizing effect on the photo-degradation of azoxystrobin, but humic acids and Fe quenched its photo-degradation. The results provided a scientific basic for rational use and environmental risk assessment of azoxystrobin.