Air conditioning (AC) system is the one with asynchronous and uncertain nature. In this paper, the fuzzy discrete event system (FDES) is introduced to the research of AC energy.saving control. A fuzzy automaton modeling is given for AC energy-saving control and effectiveness optimization is made. To facilitate the implement of the control and energy saving, priorities have been assigned to the major control steps based on logical reasoning. Forwardlooking tree modeling based on FDES has been simplified to help further optimization, and a simple and concrete example has been put forward illustrating energy-saving control in AC system.