The installation of wind turbine has enjoyed explosive growth worldwide; however, problems regarding interconnectivity to grids have arisen. It has also been pointed out that wind power generation facilities are exposed to lightning damage due to their configurations, and so different protective measures from those needed for conventional generators are necessary. This problem has recently surfaced as an important issue. Especially, Japan suffers from frequent and heavy lightning strikes, an example being the notorious ldquowinter lightningrdquo found in coastal areas of the Sea of Japan. Thus, it becomes more important to understand the grounding impedance characteristics of wind power generation from the viewpoint of lightning protection. As a report form IEC, TR61400-24, recommends a ldquoring earth electroderdquo, it seems not to be fully discussed and remains unresolved on transient behavior at a lightning strike.Therefore this report, using a finite difference time domain (FDTD) method, perform a electromagnetic transient analysis on a basement and ring earth electrode of a wind power generation in order to confirm the effect of the ring earth electrode. As the result of the analysis, it becomes clear that the ring earth electrode gives the lower steady impedance with less inductive voltage rise. Thus, it is confirmed that the ring earth electrode has certainly superiority for lightning protection.