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Pyraoxystrobin is a methoxyacrylic fungicide with low toxicity, high efficiency and broad spectrum. It has good control effect on rice blast, rice sheath blight, cucumber downy mildew and cucumber powdery mildew. In order to explo re the degradation characteristics of pyraoxystrobin in water, the hydrolysis dynamics of pyrao xystrobin at different temperatures, pH values and t he photolysis dynamics under different illumination were studied, the hydrolysis and phot olysis prod ucts and pathways of pyraoxystrobin wer e studied by mass spectrometry with 13 C-pyraoxystrobin as control. The test results showed t hat the Pyraoxystrobin was difficult to hydrolyze in acidic and alkalescent aqueous solution (pH 8. 0). In alkaline aqueous solution (pH 10. 0-13. 0), t he hydrolysis dynamics of pyraoxystro bin was affected by temperature. With t he increase of temperature and pH values, the degradation rate was accelerated. The hydrolysis rate constants were linearly positively correlated with the pH values. Hydrolysis reaction was base-catalyzed reaction, and the higher temperatures, was the higher rate constants of base catalytic reaction were. Under indoor simulated sunlight and 30 °C, pyraoxystrobin was easy to photolysis, and t he photolysis reaction rate was increased with light intensity and ultraviolet intensity. Pyraoxystro bin was difficult to photolyze under the outdoor natural light at 13-19 °C . It was speculated that the ester bond was broken on the unlabeled atom C and an alkyl group (CH3) was removed in the hydrolysis process of pyraoxystrobin. The product might be (E)-2-[ 2-[[ 3-(4-chlorophenyl)-1-methyl-l H-pyrazol-5-oxy] methyl] phenyl]-3-methoxyacrylic acid (C21 H 19 ClN2 O4). The photolysis products was presumed to be 3-(4-chlo rophenyl)-5-((2-(4-methoxyfuran-3-yl) benzyl) oxy)-1-met hyl-l H-pyrazole after car bonyl hydrogenation on unlabeled atom C, dehydration and ring formation. The hydrolysis and photolysis products of zolexin ester and 13C-pyraoxystro bin ester were analyzed by mass spectrometry. It was speculated that the hyd rolysis process of zolexin ester may be the breaking of ester bond on unmarked C atom and the dehydration of an alkyl group to form C21 H19 ClN2 0 4. The photolysis process may be carbonyl hydrogenation and dehydration on unmarked C atom. After cyclization, 3-(4-chlorophenyl)-5-[[ 2-(4-methoxyfuran-3-phenyl] methoxy]-1-methyl-l H-pyrazole (C22 H 19 ClN2 O3) was formed. In this study, 13C-labelled pyraoxystrobin was used as internal standard, the degradation dynamics of zoxomycin in water were researched at different pH values and temperatures, and the photolysis of zoxomycin in water were researched under different light conditions. The hydrolysis and photolysis products and pathways of zoxomycin were analyzed and speculated in order to provide data for rational drug use, water source protection, ecological balance maintenance and food safety. [ABSTRACT FROM AUTHOR]