Abstract: A method based on on-line purification using Accelerated Solvent Extraction (ASE) and Gas Chromatography with a Nitrogen-Phosphorus Detector has been developed to determine 20 kinds of organophosphate pesticide residues in soil samples. The temperature for solvent extraction, the type and addition method of alumina, solvent extraction system and the dosage of dispersant were studied for the determination of organophosphate pesticide in soil samples. The selected optimal extraction temperature was based on extraction efficiency and recovery efficiency. Adding acidic alumina at the bottom of the bottle could ensure the purify effect of the soil and the recovery of organophosphate. Adding the dispersant to the soil made organophosphate distribution in the soil more uniform. When the purificants were acidic alumina and graphite carbon, the temperature was 60℃, acid-alumina was added at the bottom and the volume of dispersant water was 1.0 mL, the detection limits of 20 kinds of organophosphate pesticide were 0.005-0.014 mg/L. The operation procedure was simplified and work efficiency was improved by combined processes of extraction and purification.