Abstract: An on-line pyrolysis-vacuum ultraviolet photoionization mass spectrometer was built for the analysis of pyrolysis products of tobacco. Vacuum ultraviolet photoionization is a “soft” ionization method producing few or no fragments of molecular ions, and identifing the complex pyrolysis products in real time. In this work, the pyrolysis of tobacco leaves from various stalk positions (B2F, C3F and X2F) at 300, 400, 500, 600 and 700 ℃, and the effects of reaction temperature on the pyrolysis products intensity were studied. A series of mass spectra of pyrolysis products were obtained, and the changes of products at different pyrolysis temperatures were compared. The analysis results of products at different pyrolysis temperatures were helpful to reveal the formation mechanism of compounds in different parts of cut tobacco during pyrolysis/combustion. The dynamic curves of pyrolysis products such as vinylamine (m/z 43), isoprene (m/z 68) and dimethylfuran (m/z 96) with time were further observed at 500 ℃, so as to master the dynamic change process of pyrolysis reaction. It was found that the increase of temperature can dramatically shorten the reaction time. Generally, the primary products will be formed at the medium cracking temperature, and gradually pyrolyzed into secondary products with the increase of temperature, the secondary products will be accompanied by higher temperature cracking and thermal synthesis to form tertiary products. In order to quickly screen and identify different parts of tobacco, principal component analysis (PCA) was used to analyze the mass spectra of pyrolysis products, and the differences of chemical components in different parts of tobacco were identified. Then, the components with m/z 58, 96, 110 were the typical products of X2F, the components with m/z 43, 126 were the representative products of C3F, and the main representative product of B2F was the component with m/z 84. Based on the above results, photoionization mass spectrometry was important to study the dynamic changes of tobacco pyrolysis products, the pyrolysis products of different parts of tobacco were quickly identified at 300-700 ℃, and the main pyrolysis products were summarized. By comprehensively evaluating the main components and relative content of pyrolysis products, tobacco samples from different parts can be quickly distinguished.