The invention provides an S-transformation-based lightning type identification method for a DC transmission line. The S-transformation-based lightning type identification method can determine the types of transmission line lightning bodies, that is, a lightning conductor, a lightning ground wire and a lightning pole and tower can be distinguished. The S-transformation-based lightning type identification method is based on monitoring of the travelling wave current frequency-energy relationship in transmission line conductors, and particularly comprises the following steps: acquiring travelling wave current waveform data of a transmission line; conducting S transformation analysis on the travelling wave current data, analyzing the travelling wave current frequency characteristics according to the frequency-energy distribution, and searching an upper-limit frequency and the lower-limit frequency of a main frequency band interval; determining the upper-limit frequency of the main frequency band as the characteristic quantity for lightning type identification; comparing to obtain whether the upper-limit frequency of the travelling wave current main frequency band is smaller than 38500 Hz, larger than 67500 Hz or within the range of the two identification thresholds so as to identify the travelling wave current lightning type. Compared with the prior art, the S-transformation-based lightning type identification method is definite in physical concept and explicit in judgment idea and can effectively identify the type of the lightning travelling wave current signal.