The **National Swimming Center**, locates inside Beijing Olympic Park, is one of symbolic buildings for 2008 Beijing Olympic Games. It is also called "water cube" with side of 177 m and height of 30m. The project studies the impact of envelope cavity ventilation on reducing the cooling load of the building in summer, calculates the hourly load and energy consumption, analysis the interior humidity and thermal environments and compares the reference building established by the energy saving regulation with the original design.