The spectra of artificially triggered lightning have been investigated by employing Slit-less Spectrograph in Guangdong region with the peak value of return stroke current was 183 kA, and the duration of return stroke was 45 ms. Through compared the spectrum of the metal and the air portion of the lightning channel, it was found the spectral line 4253, 4190, 4075, 5179 nm of the metal channel emission had high excitation energy, which had spectrum structure of the strong lightning channel, while the air portion had the weak lightning channel spectral structure. Through compared the relative intensity of the lines, we found the difference of relative strength of the basic lines between the metal portion and air portion is small, but relative intensity of characteristic lines of strong lightning difference was very larger. Through analyzed the excitation energy and other parameters of spectral line of the metal and the air part, the reasons of different spectral structure of the metal and air part were given. When return stroke starting, the leader channel of wire portion had not completely disappeared leading to it was further stimulated by the pulse current of the return stroke. This increased the temperature and density of plasma channel, such that the spectral line of wire portion had completely excitation by higher excitation energy. Compared with air portion, the intensity of 4075, 4190, 4253, 5179 nm had a greater increase. This result in the wire portion of the channel and the air channel had different spectral structure. Through analysis of the temperature and electron density of different channel portion which were calculated according to the information of lightning spectra, the reason why emission luminance of metal portion was different from the air portion is the radiation characteristics between the wire portion and air channel are different.