Abstract: Gas chromatography in hyphenation with mass spectrometry was applied to the determinations of volatile halohydrocarbons and chlorobenzenes in water samples.The analytes were purged and trapped,and thermodesorbed using the Trap Vocarb 3000 with high-purity helium.External standard calibration was adopted in the determination.Linear relationships between peak areas and mass concentrations of 18 volatile halohydrocarbons and chlorobenzenes were obtained in a definite range,with detection limits (3S/N)less than 0.06 μg·L-1.Tests for recovery and precision were made by standard addition method,values of recovery found were in the range of 92.6%-98.1% and values of RSD′s (n=6) were less than 8.5%.