Abstract: A method of thermal desorption gas chromatographic determination of difluorodichloro methane in air over workshop was proposed according to the requirements mentioned in reference.Difluorodichloro methane in air was sampled by active carbon,from which it was desorbed by the thermo-desorbing instrument,and introduced directly into the gas chromatograph.After separation on the FFAP column,the object compound was detected by the hydrogen flame ionization detector.Linear relationship was found in the range within 2 000 mg·L-1 (r=0.998 7) of difluorodichloro methane.Detection limit of the method was found to be 8.5×10-2mg·L-1.Precision of the method was tested at 3 different concentration levels (500,1 000,2 000 mg·L-1) and values of RSD′s obtained were in the range of 2.0%-4.6%.Permeability capacity calculated from the experimental data was 20 mg of difluorodichloro methane for each 100 mg of active carbon.The desorption efficiency for different concentration of difluorodichloromethane were all larger than 90%.The proposed method was suitable to be used for worksite monitoring of difluorodichloro methane in air over the workshop.