To actively implement the ‘Western Development’ strategy, it is essential to advance the interconnection project between Xinjiang and the main grid of Northwest China. As an important part of the transmission and substation project, the safe operation of the 750 kV double-circuit transmission line plays a vital role. As the main part of the main part of this interconnection project, the ultrahigh voltage (UHV) transmission lines are exposed to natural environmental conditions over an extended period, making lightning strikes bypass the greatest safety hazard. The existing UHV transmission line lightning shielding system is mainly based on the simplified short-gap lightning strike bypass model, which may lead to system failure during actual operation. Therefore, this paper introduces the long-gap striking distance formula and revises EGM by considering the incident angle of the lightning leader, rather than assuming it develops vertically downward when it reaches the ground. Using an example from a UHV transmission line in Northwest China, the results of the improved EGM for calculating the lightning shielding failure rate are compared with those from the classical EGM to validate its applicability to UHV transmission lines.