In view of the situation that the ultra-high lightning rod systems are increasing, but the overall interception performances of them are difficult to be effectively evaluated by current standards, a numerical evaluation method for the interception performance of surface objects or devices is developed based on the subgrid technology. The numerical evaluation model of the interception performance for the ultra-high lightning rod system is proposed, and the numerical evaluation experiment for the interception performance of the typical ultra-high lightning rod systems is carried out. The results show that the interception probability at the top of the air-termination system is the highest, but other parts of the upper part of the air-termination system can also be subjected to side flash. The probability of side flash that occurs on the upper part of the air-termination system increases with the height increase of the side flash point. Moreover, the intensity of lightning or thundercloud can also affect the interception probability of different parts of the air-termination system. The smaller the intensity of lightning or thundercloud, the lower the interception probability of the top of the air-termination system, the greater the probability of side flash that occurs on the air-termination system. And the coverage of the side flash points will also gradually expand to the lower part of the air-termination system.