Abstract: Determination of 9 organochlorine pesticides (usually in trace level) is necessary for water and soil quality evaluation in geological survey project. Based on the large amounts of the analytical data of organochlorine pesticides in groundwater and soils from geological survey project and authors' practical experiences, the measures to improve the sensitivity and accuracy for the determination of organochlorine pesticides in groundwater and soils were discussed. The response values of target compounds were improved by use of silica wool and selection of the injection solvent. And using GC-MS/SIM in judgement and elimination of false-positive results were also discussed in details.