Abstract: The application of a newly homemade instrument system for volatile organic compounds (VOCs) online monitoring was described, which included an online double-channel and two-stage cryogenic concentration system and a comprehensive two-dimensional gas chromatograph-time of flight mass spectrometer. The ambient air was sampled into the trap tube. The VOCs in the air including hundreds of species in C2-C12 were trapped and enriched using the cryogenic enrichment module, which had an ultralow temperature of -160 ℃, then separated and detected by comprehensive two-dimensional gas chromatograph-time of flight mass spectrometer for C3-C12 compounds and by gas chromatograph with flame ionization detector for C2-C4 compounds. The system was tested in performance using a mixed sample of standard gas of PAMS and TO-15 (108 compounds totally). The results showed that 108 compounds in gas could be separated into each compound clearly. The limit of detection for 97.2% of compounds was less than 1.0×10^-10mol/mol, and the linear correlation coefficient computed from the quantitative standard curve R2 of 94.4% of compounds was larger than 0.99, meanwhile the relative standard deviation (RSD) of 96.3% of compounds was less than 10%, which made it satisfactory for the monitoring requirements of VOCs in air. In addition, the performance of the system was contrasted with normal gas chromatograph-mass spectrometer with the same standard gas and actual gas. The results indicated that comprehensive two-dimensional gas chromatograph-time of flight mass spectrometer could get better limit of detection and the separating capability, the performance of this system was much better in qualitative and quantitative accuracy and in sensibility and in interference elimination ability, which was beneficial for samples with complex composition. Coupled with a VOCs concentration system and a comprehensive two-dimensional gas chromatograph-time of flight mass spectrometer, the system is a powerful tool for solving the problem of complex sample system analysis, and will works in the field of complex VOCs monitoring in air.