Abstract: The organochlorine pesticide residues in lettuce were extracted using supercritical CO₂ as pretreatment method.The extraction conditions were optimized by orthogonal experiments with the pressure,temperature,flow,time as influencing factors and recovery rate as the evaluation index. Gas chromatography was applied to determine the content of organochlorine pesticide residues.The results showed that the recovery of each pesticide residues reached maximum when the extraction pressure was 30 MPa,the temperature was 50 ℃ and the flow rate was 1.5 m L / min,extraction time was 20 min,and the recovery rate was higher than 80%.The optimum conditions of this experiment was suitable for pretreatment of organochlorine pesticide residues in lettuce,and this method was more convenient and quick,compared with the national standard method.