Due to the lack of adequate studies on the characteristics of infrared spectra of oil flame, an analytical study on flame spectra of various oil types and other combustible objects in outdoor space is carried out by establishing an all-flame infrared testing system with the spectral range of 1~14 mm. The results show that the signal of honeycomb briquette spectrum is the most special among all the spectra. After 5-layer decomposition of other fuel flame spectral signals by the db2 mother wavelet, low frequency components of 92# gasoline, 95# gasoline, 0# diesel oil, aviation kerosene and lube flame spectral features are similar and there exist strong emission peaks in the vicinity of 1.2, 3.4 and 4.5 mm. The 5th layer detail coefficients of various fuel oil flame are in line with each other. The low frequency components and the detail coefficients of 92# gasoline and 0# diesel oil flame spectra have obvious features compared with those of other fuels (wood, alcohol and paper). The experimental conclusion is of great significance in the detection and identification of oil flame based on spectral characteristic analysis.