For lacking an accurate method of protection range calculation for the rolling sphere method in the lighting protection standards, a simple calculation method is presented, which is more precise, and easier and more convenient to use, better than the graphing method. A thorough analysis is made of the judgment of the protection range of the double lightning rods for any point from the aspects of both the influence scope of a single lightning rod and the coaction scope of the doublerod lightning protection. The method is devised through analyzing the judgment methods of protection range of two lightning arresters on buildings by means of both distance comparison and angle comparison methods. The calculation method can be applied easily in lighting protection service.