Abstract: The factors affecting the quantitative accuracy of GB/T 5750.8—2023 for the determination of chloroform and carbon tetrachloride in drinking water by headspace-gas chromatography, such as split ratio, chromatography column, matrix blank and standard curve preparation, etc., were discussed. And the conditions were optimized by combining with the 7697A headspace autosampler, the 7890B gas chromatograph and the DB-1701 quartz capillary column (30 m×0.25 mm×0.25 μm). The method was confirmed by the optimized experimental conditions, and the linearities of chloroform and carbon tetrachloride were good in the range of 0.1~10.0 μg/L and 0.01~1.0 μg/L, respectively. The limits of detection were 0.025 and 0.0020 μg/L, the limits of quantification were 0.083 and 0.0067 μg/L, respectively. And the correlation coefficients were greater than 0.999, the relative standard deviations were 4.2%~6.5% and 1.8%~4.0%, and the recoveries were 96.8%~102.5% and 104.0%~107.2%, respectively. The optimized method can meet the requirements for the determination of chloroform and carbon tetrachloride in drinking water, and provide a reference for the testing of trichloromethane and carbon tetrachloride in water.