Due to the expansion of EHV/UHV transmission lines，the probability of lightning strike on the line is increased， and the tower of the same line may be in different working environment． Therefore，it is necessary to study the influence of grounding resistance on lightning resistance performance of the lines． The back － flashover model for three kinds of towers are established，such as cat － head type tower，cup type tower and drum － shaped tower of 500 kV AC transmission lines． The influence regularity of grounding resistance of three models on lightning back － flashover performance is analyzed，that is，the flashover rules of cup type tower is similar to the drum － shaped double － circuit tower，and it has the greatest influence on the drum － shaped single － loop，followed by the drum － shaped double － circuit and the cup type tower，and it has the least influence on the cat － head type tower．