Abstract: By introducing an abnormal heating fault of a 220 kV voltage level line lightning arrester discovered by the online monitoring system, and conducting diagnostic analysis such as DC reference voltage and leakage current tests, infrared temperature measurement under operating voltage, resistive current tests, and power frequency reference voltage tests on the abnormal lightning arrester, it is ultimately determined that the abnormal cause is caused by moisture inside the epoxy resin insulation cylinder of the lightning arrester, And propose follow-up handling suggestions and measures.