The thermal decomposition properties of hexafluoropropane clean gaseous fire-extinguishing agent were studied in tubular reactor from 500 to 750 ℃ and the decomposed gas was characterized by gas chromatography(GC), Fourier transform infrared spectroscopy(FTIR) and gas chromatography-mass spectrometry(GC-MS). Hydrogen fluoride was detected after the decomposed gas was analyzed by pH testing, while pentafluoropropylene was found by GC-MS. The results showed that hydrogen fluoride eliminated from hexafluoropropane was the main reaction, while pentafluoropropylene was the primary product during hexafluoropropane decomposition under high temperature. GC and FTIR results indicated that the reaction temperatures had significant effects on the thermal decomposition of hexafluoropropane. Haxafluropropane was steady at 500 ℃, whereas started to decompose weakly at 600 ℃. The degree of the thermal decomposition of hexafluoropropane was enhanced with the temperature increase. And hexafluoropropane underwent intense decompositon at 750 ℃. FTIR can be used as a new method to study extinguishing mechanism of fluorine-containing fire extinguishing agent online.