Abstract: The degradation efficiency of malathion by high voltage electric field cold plasma was studied by using the high-voltage electric field voltage intensity,treatment time and initial concentration of pesticide as experimental parameters. Gas chromatographic(GC)was used to determine the residue of malathion and a degradation kinetic model was established. Gas chromatography tandem mass spectrometry(GC-MS)was used to identify malathion degradation products. Combined with Fourier transform infrared spectros’copy(FT-IR),the degradation efficiency of malathion by cold plasma was studied and its degradation pathway was analyzed. The results showed that the degradation efficiency of malathion in water significantly increased with the increase of cold plasma voltage intensity and treatment time(P<0.05). When the initial concentration was 0.1 μg/mL,the degradation efficiency of malathion reached 79.62%±2.97% by the treatment of 50 Hz,80 kV for 180 s. The degradation products were malaoxon,triethyl phosphate,2-butenedioic acid(Z)-,diethyl ester,2-butenedioic acid(E)-,diethyl ester,O,O,S-trimethyl phosphorodithioate and 2-dimethoxyphosphinothioylsulfanyl-4-ethoxy-4-oxobutanoic acid. Malathion could be degraded into triethyl phosphate with lower toxicity by further processing. And the formation of intermediates in the degradation of malathion mainly by two pathways of oxidation of P=S bond and fracture of C-S bond. The study provides a new method for the study of degradation of pesticide residues in water.