Trace sulfur dioxide in ambient air was adsorbed and enriched by themal desorption gas chromatography. The sample passed through a thermal desorption tube filled with Tenax TA at a flow rate of 200 mL/min for 10 minutes. After desorption at 300 ℃, the sample was sent to the gas chromatograph and detected by flame photometric detector. The standard curve was established with sulfur dioxide standard gas in nitrogen for quantitative analysis. The results showed that the linear range of sulfur dioxide was 47.0~960 nmol/mol and the quantitative repeatability was 6.6%. The detection limit was 3.1 nmol/mol and the linear correlation coefficient (r) was 0.998 3. Inorganic sulfide and other inorganic gas did not interfere with the detection. The linear correlation coefficient (r) between this detection results and the trace sulfur dioxide monitoring results of the atmospheric automatic station was 0.91. There was no significant difference between the variation of monitoring values and the analysis values with time.