Abstract: The analysis of Volatile Organic Compound(VOC) in room and outside air has been carried out widely among academic institutes,colleges,universities,as well as environment protection and health epidemic prevention system.The difficulty of this task consists in the complicated composition and small content of VOC in the air sample to analyze.Especially,the VOC in room air is very thin generally and can not be tested by gas chromatography without condensation.Therefore,the condensation method becomes the key of VOC gas chromatography.We developed a new one-time thermal desorption and direct sample injection thermal desorption instrument,and it has been put into practice largely.There are backflush unit and injection port in the instrument,through which desorption pipe can be conditioned and standard curve can be drawn easily.The thermal desorption pipe is equipped with gas path.Hot desorption pipe could be cooled to room temperature by opening the thermal desorption stove lid in just 4 to 5 minutes. The quantitative analysis performance of the instrument,such as repeatability, accuracy,thermal desorption ratio and linearity was tested.Practical sampling analysis has showed that it is a fine method due to high sample condensation multiple,simple operation,good repeatability,high accuracy and credible analysis result.It suits the test of samples in bulk.