The experimental adopts Headspace - Gas Chromatography method on analyzing 1-chlorobenzene in water sample, which optimizes pre-treatment and GC condition of Headspace - Gas Chromatography. The method could achieve the minimum detectable concentration to 0.005mg/L, the relevant linear correlation coefficient of standard curve to 0.9999, the linear range between 0.1 mg/L to 2mg/L, the average added recovery between 101.4% to 103.4%, and the relative standard deviation between 1.6% to 6.94%. The method fits the detection of 1-chlorobenzene in water with simple operation, good reproducibility, and low detectable concentration.