In order to improve the performance of electric transmission line protecting around hit lightning

this paper focuses on the analysis method of the high voltage transmission line about the lightning protection performance of shielding failure.According to the EGM in which the striking distance factor K and ground obliquity θ is considered

it takes the intersection of transmission tower central line and ground as reference point

and then derives the calculation method of the maximum striking distance.It also discusses the relationship among the striking distance factor K

protection angle of lightning conductor α and ground obliquity θ when the maximum striking distance does not exist

and demonstrates that the lightning protection performance of shielding failure can be enhanced effectively through the balance of K

α

and θ.