The pyrolysis characteristic of phenolic foam was investigated by use of thermogravimetry Fourier transform infrared spectrometry mass spectrometry（TG FTIR MS）. The results show that pyrolysis process can be divided into three stages. At the first stage, the mass loss rate is low, and the gases of small molecular mass, such as H2O and HCHO, escaped physically. The second stage is the beginning of pyrolysis reaction, at which H2O, HCHO, CO2, SO2, SCH4（methanethiol） and C2NH5（aziridine）are produced. At the third stage, the main chain fractures and pyrolyses, CO2 is spawned. Generation rate of C2NH7（dimethylamine）, CH2O2(formic acid), HCHO and C2NH5 reach maximum. At 42558℃ the mass loss rate attain maximum, -14787%/min. The pyrolysis reaction of phenolic foam in this stage is the most violent. The sum of mass loss at the second and third stage is 84% of the whole mass. The whole process of mass loss ends at 56520℃.