The building energy consumption is one of the major problems concerned by all the countries in the world. In the integral building systems,the consumption of the HVAV systems is more than 35 percent of the total building consumption. So it is important to study the strategies of energy_saving for air_conditioning systems. This paper explains some efficient and energy_saving HVAC systems, such as ice_storage air_conditioning system and underfloor air_conditioning system,and presents the strategies to accomplish the energy_saving purpose by using materials of energy_saving for enclosure structure and proper control systems. Some problems on the conservation of design and the difficulties in practical operation of energy_saving air_conditioning systems in exiting are discussed.