Abstract: The sample of hydrogen system was taken as the investigation object, and sub-atmospheric sampling was used. Before analyzing the sample, the whole injection pipeline was purged and cleaned 3 times, and then kept in vacuum. The injection pressure of the sample was adjusted by valve injection, and oxygen, nitrogen, carbon monoxide, methane were determined by gas chromatography with helium ionization detector. As shown by the results, linear relationships between injection pressure of the sample and values of peak area of 4 components were kept in the range of 10 100-101 225 Pa, with detection limits (3S/N) of 4.0, 3.8, 5.2, 3.6 nmol·mol^-1, respectively. A set of mixed standard gas were analyzed 6 times in parallel by the proposed method, with RSDs of values of peak area in the range of 0.011%-0.72%. Another set of mixed standard gas were analyzed by the proposed method, and the determined values were in accordance with the known values. In addition, the sample amount of sub-atmospheric sampling was only 1/4 200 of that of normal (positive)-atmospheric sampling, and the total time consuming of determination process was only 1/3 of that of normal (positive)-atmospheric sampling.