Abstract: Due to constantly appearing of extreme weather in recent years, it leads to a big difference between the previous statistical law and trend of lightning and the current actual situation, and it brings obvious error in to the lightning protection evaluation of transmission lines. By means of analyzing the ground lightning data within the scope of 10 km width of dozens of 500 kV transmission line corridors in Central China, the relevant law of thunder discharges in these regions, which were divided into three types, i.e., the main discharge containing subsequent return stroke, the main discharge not containing subsequent return stroke and subsequent return stroke, was analyzed, and it was discovered that the times of the main discharge containing subsequent return stroke was the least. It was discovered also by analyzing the ground lightning with different polarities that the proportion of negative polarity discharge obviously varied with statistical patterns of discharge types, and in the total amount of the positive polarity discharge the proportion of the main discharge not containing subsequent return stroke was 79.33%. On the basis of above-mentioned analysis, the entropy weight method, by which the influences of the parameters of both main discharge and the subsequent return stroke on transmission line trip could be considered, was proposed. The weighted calculation results of practical transmission line show that the lightning trip of practical transmission lines is mainly caused by main discharge containing subsequent return stroke as well as the subsequent return stroke, thus, the proposed entropy weight method turns out to be true.