Abstract: The method mentioned by the title was proposed after optimizing headspace conditions of the equilibrium temperature, equilibrium time, and sampling volume by orthogonal experiments. The sample of benzylated quaternary ammonium salts was diluted with ethanol to a 300 g·L⁻¹ sample solution, and an aliquot (4 mL) was taken and placed into a headspace bottle. The mixed solution was equilibrated at 90 ℃ for 20 min, and the gas obtained was introduced into a gas chromatograph. Benzyl chloride was separated on a DB-WAX UI capillary column under programmed temperature conditions, with external standard method for quantification. It was shown that linear relationship between values of the mass concentration and peak area of benzyl chloride was kept in the range of 10−110 mg·L⁻¹, with the detection limit (3s/k) of 3.73 mg·L⁻¹. RSD of the determined values was 1.3% from 6 repeated tests on the sample of dodecyldimethylbenzylammonium chloride (1227). Test for recovery was conducted at the 3 spiked concentration levels on the 1227 sample, and recoveries of benzyl chloride ranged from 104% to 107%. The proposed method was used for three 1227 samples and one octadecyldimethylbenzylammonium chloride (1827) sample. Benzyl chloride was detected in one 1227 sample, with the detection amount of 177 mg·kg⁻¹.