With the large number of power electronic devices applied to the power grid, the advantages of transient protection are more obvious. For the problem that it is susceptible to lightning strikes, the additional component of transient current in each phase are analyzed under short-circuit fault, lightning strike disturbance and lightning strike causing fault. The essential difference between fault and disturbance is whether the trend of the transient waveform has the characteristic of power frequency sine wave. Accordingly, the method of using the average value sliding denoising can eliminate the high frequency effects such as lightning current, and obtain the main waveform. It is proposed to fit the main wave with a 50 Hz sinusoidal function. Based on the determination coefficient criterion of fitting, the faults and lightning strike disturbance of each phase line can be distinguished. The PSCAD/EMTDC electromagnetic transient simulation results verify that the proposed identification scheme can correctly identify lightning strikes and faults under various scenarios. It is suitable for various transmission lines without being affected by the inception angle of the fault and the transition resistance. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900604) and National Natural Science Foundation of China (No. 51637005).