With small-scale oil pool experimental and spectral analysis method, the flame spectrum in initial stage of 0# diesel oil combustion was conducted a preliminary study for the first time, which was used to develop the technique of intelligent identification and suppression of fire extinguishing at the initial stage of diesel oil combustion. It educed the overall characteristics flame spectrum at the initial stage of 0# diesel oil combustion: in 200～380 nm wavelength of near-ultraviolet bands, the spectral intensity is the weakest, the spectral intensity does not change with wavelength, the number of characteristics spectral bands is minimum, the number of obvious characteristics spectral peaks is almost none; in 380～780 nm wavelength of visible bands, the spectral intensity is the strongest, the spectral intensity increases with wavelength, the number of characteristics spectral bands is maximum, the number of obvious characteristics spectral peaks is large; in 780～1 100 nm wavelength of near-infrared bands, the spectral intensity is relatively strong, the inflection point of spectral intensity appears in 780 nm, the appeared intensity decreases with wavelength, the number of characteristics spectral bands is relatively large, the number of obvious characteristics spectral peaks is at a certain number. It is educed through further analysis of the flame spectrum that: the primary intermediate radicals includes OH, CN, CH, C2, H2O, etc; the primary characteristic spectral bands includes the OH racial bands of 3 064  System and Vibration-Rotation bands, the CN racial bands of Violet System and Red System, the CH racial bands of 4 315  System, the C2 racial bands of The Swan system and Phillips Near Infra-red System, the H2O molecular Vibration-Rotation bands, etc; the bands and time distribution of primary intermediate radicals and its main generation mechanism; the existence of potassium in this experimental batches of 0# diesel oil and the spectral peak of spectral lines in 766 and 769 nm is obvious; the peak of spectral intensity in 431, 512, 516, 547, 589, 766, 769, 891, 927 nm is obvious, and it suitable for the sign of flame identification at the initial stage of 0# diesel oil combustion.