Abstract: In order to evaluate the properties and variations of chemical structures of pyrolyzed tobacco, real-time temperature-rising infrared spectrometry (RTR-IR) was applied to the online detection and analysis of flue-cured, burley and oriental tobacco, expanded tobacco, expanded cut stem and reconstituted tobacco at different pyrolysis temperatures. The results showed that: 1) The intensity variations of the same functional group in different tobacco samples differed slightly, while the intensities of different functional groups in the same sample differed significantly along with the change of temperature. 2) At the first main temperature interval of mass loss of tobacco (150℃-400℃), O-H, N-H, C-O, and C-N bonds degraded totally and there was only a trace of C=O bond left, accompanied with a great amount of aromatic components formed,which became the primary functional groups in the char together with the C-H bond. The oxidative degradation of C-H bond and aromatic components principally occurred at the second temperature interval of mass loss (400℃-570℃). At the same time significant heat was released. The endothermic formation and transformation of inorganic salts were the main chemical reactions above 600℃.