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This thesis studies the lightning protection of a 220 kV double-circuit overhead transmission line installed on a single steel tower. An EMTP-RV model was established based on the parameters of the P220kV-2 tower, conductors, shield wire, insulator strings, grounding resistance and line surge arresters. Two lightning conditions were considered: lightning stroke to the tower and direct lightning stroke to the phase conductor. The unprotected line was first analyzed to determine the most vulnerable phase and the critical lightning current. The results show that the lower phase has the lowest critical lightning current. Then, 220 kV line surge arresters with a spark gap were added to the model. The simulation results indicate that the arresters can effectively reduce lightning overvoltage and decrease the risk of insulator flashover, especially when the tower grounding resistance is high.