The global optimization model for the overall control of air-conditioning system aiming at the minimum energy consumption is developed in this work. The method of decomposition-coordination, which is adept at solving the ultrahigh-dimensional optimization problems, is used for the model solution. Taking one real central air-conditioning system as the case study, the hourly optimal conditions of all equipments in this system on one operation day were simulated by the global optimization model. To examine the validity of decomposition-coordination algorithm, direct-search method (which is admitted to be the most reliable in optimization calculation) is used to make the comparison. It showed that the optimal results obtained by the two methods were essentially the same, but decomposition-coordination method would have much higher calculation efficiency than direct-search method. The energy analysis indicated that the energy saving brought by the global optimization was mainly thanks to the adjustment of pumps and fans rather than that of the chillers. It was believed as well that more energy saving would be achieved under the lower load condition of the system if the globally optimal control scheme were implemented. (C) 2009 Elsevier B.V. All rights reserved.