Exploration is made of the solution for computing the protection coverage of multiple unequalheight discharging rods by means of a mathematical method, and the mathematical solution to the problem is presented, which set the theoretical basis for computer programming for solving the problem. The establishment of the mathematic model for computing the position of the virtual ball supported by three unequalheight discharging rods is the key to the problem. Because the position of the rod tips is known, the quadratic equations with three variables are established according to the related geomorphic principles to obtain the protection coverage of discharging rods. A brief analysis is also made of the computation of the mounting height of the lightning protection belt according to the principles of the rollingball method.