Abstract: Lightning is one of the common factors causing faults in overhead transmission lines. This paper focuses on the analysis of a lightning fault on a 35 kV transmission line in Beijing area. The introduction and analysis are mainly conducted from the aspects of line conditions, fault conditions, on-site investigation, and testing. Based on the investigation and testing results, the cause of the fault is analyzed. It is found that after the line is struck by lightning, the air gap between the counter lead of the lightning arrester and the extension rod of the lightning arrester is too short due to the excessive length of the counter lead, leading to breakdown. Finally, corresponding improvement measures are proposed.