Abstract: A method of headspace-solid phase microextraction combined with gas chromatography-mass sepctrometry was applied to determination of 4 kinds of trihalomethanes (CHCl₃、CHBrCl₂、CHBr₂Cl、CHBr₃) in drinking water. The water sample (25 mL) was added into a 40 mL headspace vial and adjusted to pH 8.0 with 0.2 mol·L^-1 HCl solution. Then 0.20 mL of 20.0 mg·L^-1 1,2-dibromopropane solution as internal standard and 7.0 g of sodium chloride were added, and the mixture was extracted with a solid phase microextraction apparatus at 30℃ for 30 min and the analytes were determined by gas chromatography-mass spectrometry after being deposited at 250℃ for 50 s. A TG-5MS chromatographic column (30 m×0.25 mm, 0.25 μm) was used for separation. Electron bombardment ion source and selective ion monitoring mode were selected in mass spectrometry. The same linear range of the 4 kinds of trihalomethanes was 10-160 μg·L^-1, and the detection limits (3S/N) were in the range of 0.16-0.26 μg·L^-1. Values of recovery obtained by standard addition method ranged from 95.8% to 120%, and the relative standard deviations (n=5) of the measured values ranged from 1.4% to 15%. The method was applied to determination of the 4 kinds of trihalomethanes in 15 drinking water samples from 5 cities in Inner Mongolia, giving mass concentration in the range of 8.31-81.14 μg·L^-1. CHBr₂Cl was the most important carcinogenic factor and the total cancer risks of the 5 cities were 5.12×10^-5, 3.82×10^-5, 5.84×10^-5, 5.53×10^-5 and 6.25×10^-6, respectively.