This study employs gradient method (GM) to solve economic dispatch of chiller plant (EDCP) problem. GM overcomes the flaw that with the Lagrangian multiplier (LM) method the system may not converge at low demand. In this study, the load balance constraint and the operating limit constraints of the chillers are fully accounted for. After analysis and comparison of the two cases studies, we are confident to say that this method not only solves the problem of convergence, but also produces results with high accuracy within a rapid timeframe. It can be perfectly applied to the operation of air-conditioning systems. (C) 2009 Elsevier Ltd. All rights reserved.