Abstract: Purge and Trap-gas chromatography-mass spectrometry (P&T-GC-MS) was established to determine the content of trimethylamine in ambient air and exhaust gas. A sampling tube containing glass beads treated with oxalic acid was used to collect 10 L of gas sample at a flow-rate of 0.5 L·min^-1. The trimethylamine in the gas sample reacted with oxalic acid to form trimethylamine salt attached to the surface of the glass beads. The glass beads were transferred to the purge bottle, and 3.0 g of potassium hydroxide and 5 mL of water were added to promote to desorb the trimethylamine gas, which was trapped and desorbed under optimized P&T conditions and subsequently analyzed by GC-MS. rtx-624 column was selected for chromatographic separation with split sampling and programmed temperature mode; In MS analysis, EI ion source and SIM mode (m/z 58, 59, 42) were adopted. As shown by results, the mass of trimethylamine and its corresponding chromatographic peak area showed a linear relationship within 0.05-2.00 μg, and the instrument detection limit (3S/N) and method detection limit (3.143s) were 1.0, 1.2 μg·m^-3 at the sampling volume of 10 L respectively. A spiked test was made by addition of trimethylamine standard solutions to nitrogen at 3 concentration levels, giving recoveries in the range of 92.0%-112%, and RSDs (n=6) found were ranged from 9.4% to 26%. The proposed method was used to analyze the exhaust gas in three periods collected at the exhaust gas treatment tower and the ambient air at the sewage treatment plant boundary, and the results showed that the highest value of trimethylamine emission of exhaust gas was 0.017 kg·h^-1, lower than the limit of trimethylamine emission (0.54 kg·h^-1) for 15 meters exhaust cylinder described in GB 14554-1993; and value of the trimethylamine in the ambient air was 3.2 μg·m^-3, less than the limit of unorganized emissions of the plant boundary (0.05-0.80 mg·m^-3) specified in GB 14554-1993.