The high-frequency component caused by lightning strokes on UHVDC transmission lines is the main factor of the mis-operation of travelling wave protection and transient protection. Due to the existence of fault current pathway to the earth, when lightning strokes failures and the common earth faults occur on the transmission lines, the voltage amplitude of the signal attenuates quickly, thus with a low signal complexity. While lightning strokes occur without forming faults, there is no fault current pathway to the earth, the signal attenuates slower, thus with a high signal complexity. Based on the wavelet transform analysis of the attenuation of voltage signal, this paper shows the ratio of data-windows before and after the mutation moment to describe the change of signal complexity. With the combination of high-frequency component content analysis of the voltage signal, the identification of lightning transient signal is achieved, and the faulted line is selected by the energy relative entropy. Based on the model built on PSCAD/EMTDC, the results show that the scheme identifies the transient signals effectively with less influence by the fault distance and the transition resistance, etc. This work is supported by National Key Research and Development of China (No. 2016YFB0900604) and State Grid Zhejiang Corp Science and Technology Project (No. 5211MR160006).