The invention provides a building lightning protection range determining method, comprising: determining ball radius of a lightning rod according to building lightning arrest level so as to determine a protection range for each lightning rod acting as an independent lightning rod; determining a surface independent protection range circle of each lightning rod and a building height level independent protection range circle of each lightning rod according to the protection range of each lightning rod acting as the independent lightning rod; determining a joint protection range envelope curves of all lightning rods around a building in the building height level; monitoring whether the current building lightning protection range is feasible or not according to whether the building height is within the joint protection range of any two lighting rods or not. Three-dimensional ball concept is simplified as two-dimensional planar drawing method, and drawing results are vivid, simple and clear.