The pretreatment process of organo-phosphorus pesticides wastewaters by wet air oxidation was studied in a 2L autoclave, using the wastewater from o,o-dimethyoxy-thiophosphoryl chloride production. The optimal combinations of process conditions were ascertained to get or gano-phosphor us removal of 80-90%,COD removal of -60%.Process conditions were reson-able mild. After pretreatment the biodegradability of wastewaters was obviously enhanced, The BOD5/COD ratio was increased from 0.2 to 0.4-0.5. Good result...