Objective To investigate the degradation of methamidophos pesticides in wastewater by ClO2 oxidation. Methods The effects of traditional activated sludge degradation method and ClO2 oxidation treatment on methamidophos pesticide wastewater were compared to study the effect of ClO2 dosage on the change of chemical oxygen demand (COD) value in methamidophos-containing pesticide wastewater. Results The removal rate of COD in methamidophos pesticide wastewater increased steadily with the increase of ClO2 dosage and the aeration time. When 20 mL of wastewater was oxidized with 25 mL of ClO2 for 5 min, the COD decreased from 7 697.31 mg/L to 391.2 mg/L, and the removal rate reached 94.92%. After fitting, the regression equation for the treatment of methamidophos wastewater by ClO2 is: y=0.98x3-32.63x2-83.23x+7626.60, R2=0.98, where x is the amount of ClO2 (mL) and y is the remaining COD value (mg/L) ). The methamidophos-containing pesticide wastewater was degraded by conventional activated sludge degradation method for 204 h. The COD decreased from 8 230 mg/L to 1 451 mg/L, and the removal rate was 82.37%. Conclusion Compared with the traditional activated sludge degradation method, the ClO2 oxidation method requires a short time, high COD removal rate, and no secondary pollutants such as chlorinated organic compounds. ClO2 oxidation is a desirable method for the treatment of methamidophos pesticide wastewater.