The invention discloses a lightning prevention device for protecting an AC electric railway traction power supply system, which comprises an upright column, wherein a wrist and arm insulator is fixedly arranged on the upright column; the high-voltage side of the wrist and arm insulator is connected with the power supply system, and the low-voltage side is connected with the upright column. The lightning prevention device is characterized in that both ends of the wrist and arm insulator are respectively provided with a hoop assembly; the upper parts of the two hoop assemblies are respectivelysymmetrically provided with a lightning arrester body; the upper parts of the two lightning arrester bodies are respectively symmetrically provided with a cavel electrode, and an air clearance is formed between the two cavel electrodes; and the cavel electrodes are made of stainless steel materials. The invention has convenient installation, high reliability and favorable corrosion resistance andelectric arc ablation resistance of the cavel electrodes and can effectively prevent the insulator from generating flashover breakdown and protect the running safety of the railway traction power supply system.