The large multi-chiller system is commonly used in the semiconductor factories and electronics factories, it is one of the department consumed a great deal of energy in factory. Therefore, it is worthwhile to design the chilled water system operation. In this paper, a design methodology is developed for multi-chiller system in which chiller units consist of different cooling capacities chiller that run in parallel. The optimal integrity scheme can be obtained using the MINLP method which minimizes the system energy consumption within a future time period. Instead of a lag scheme used in the general method, this forecasting scheme provide a integral optimal schemes within a future time period and offers the operating reference for operators.