To analyze the lightning shielding performance of UHV transmission lines in China more accurately, based on the long air gap discharge test data and lightning return stroke observation data in China, an improved EGM model suitable for lightning shielding performance evaluation of large-scale transmission lines considering terrain conditions is established and verified. The strike distance formula is modified to rs = 0.13(I 2+ 40I)0.814. The calculation results of lightning shielding failure rate of three-phase conductors of EHV and UHV transmission lines by the improved EGM model are consistent with the lightning observation data of actual lines in Japan and the lightning simulation test data of UHV transmission lines in plains and mountains of China. This verifies the applicability of the improved EGM model. The improved EGM model is used to evaluate the influence of tower type and slope steepness on shielding failure trip rate of UHV transmission lines. The results show that the shielding failure trip rate of SZ322 tower is higher than that of SZT1 tower, and the shielding failure trip rate of a UHV line increases with the increase of slope steepness. The correction of the EGM model and the optimization of calculation method in this paper have a certain guiding significance for the design of lightning shielding performance of UHV transmission lines in China. This work is supported by the National Natural Science Foundation of China (No. 51807113).