Abstract: Purge and Trapping-Gas Chromatography-Mass Spectrometry was used to determine volatile organic compounds in water. The accuracy of the quantitative analysis was affected by several factors, including standard preparation, preservation of samples and standard solution, and gas purity during analysis, sample bottles should be kept as clean as possible to avoid pollution. The preservation of samples and standard solution over long time can reduce the recoveries of target compounds. Impurities arise from the carrier gas and sweep gas and the separating degree affects the accuracy of the measurements of peak height and peak area, which consequently affects analysis precision. The solution to this problem is presented in this paper. Selected ion monitoring (SIM)was chosen generally, and a quantitative ion was selected according to the matrix. The initial temperature was dropped to 40℃, and maintained for 2-3 minutes, in order to assure the recovery of vinyl chloride. The laboratory should have a good ventilation environment to avoid cross contamination from methylene chloride. The highest temperature of the chromatographic column was increased to 220℃, and maintained for 2-3 minutes, in order to ensure the continuity of the analysis and eliminate interference from alkanes and naphthalene. For turbidity samples, an on-line filter in the field or using Static Headspace-Gas Chromatography technique directly is recommended.