As a widely existing problem in current designing of air-conditioning system, excessive designing cooling load has caused considerable surplus in water chiller capacity and serious waste of resources. Surveys show that, in some projects, even in the hottest seasons, one third or even one half of the water chillers are not in operation [1]. In order to solve this problem, expert system technology in artificial intelligence is introduced and incorporated with the air-conditioning load index assessment method. Consequently, calculation expert system of air-conditioning system’s designing cooling load is established on the basis of artificial neural network theories. Practical examples indicate that this system is simple and workable; the calculation results thereof achieve high accuracy, and calculation methods are in conformity to the thinking habits of air-conditioning designing personnel.