Considering the importance of 500 kV line and taking 500 kV transmission line in Chongqing as an example, the authors calculate lightning strike outage rate (including return stroke and lightning shielding failure) using regulation method, outage rate of return stroke using travelling wave method, and outage rate of lightning shielding failure using EGM. By comparing and analysing the calculating fesults, weakness of insulation and the area of easy to striking are found out, and corresponding improving measure is brought forward. The results show bigger gradient of lightning higher return stroke tripping, and in regulations result of accounting return stroke tripping is more closed to practical experience, accounting shielding failure rate exists obviously defect, and in EGM accounting shielding failure rate have take much factor, result is more close to practical experience.