With the increment of circuit number in the transmission lines with four-circuit on a tower, the height and width of tower would increase obviously, which could largely influence the lightning withstand performance of the line. In order to accurately assess the lightning withstand performance of both horizontal and vertical tower, the improved electric geometry method(EGM)model and elector-magnetic transient program (EMTP)are applied to calculate the lightning withstand performance of the two tower type under different ground dip angel and grounding resistance. The results show that the lightning performance of horizontal tower is much better than the vertical one. Therefore, it is highly recommended that horizontal tower be applied in mountain area or serious lightning area, while the vertical tower be applied in the area where the line corridor is scarce.