Portable gas chromatography-mass spectrometry (GC-MS) can simultaneously carry out qualitative and quantitative analysis of multi-component complex organic compounds. Because of its characteristics, portable GC-MS plays an increasingly important role in environmental monitoring, especially in the spot emergent monitoring. In this study, performance of portable GC-MS on determination of low concentration of volatile organic compounds (VOCs) in ambient air was compared with EPA TO-14A method, and the accuracy of high concentrations of VOCs determined by loop ring model was examined. Results indicated that detection limits of VOCs in air HAPSITE portable GC-MS was equivalent to that of EPA TO-14A method, while accuracy and precision is slightly lower, but all accord with the requirements of environmental monitoring and analysis. The loop ring can be used in the emergent pollution accidents for it can accurately analyze samples in high concentration of VOCs in the grade of 10(-6).