In these days, the cooling load in homes has increased with the IT revolution, and people have paid more attention to energy conservation during the summer. In order to cut down the energy consumption for air conditioning, the displacement ventilation system, which supplies cold air directly to the occupied zone, has been adopted in the experimental house in Kitakyushu. Compared with the conventional mixing system, the characteristic of cooling load of displacement system is analyzed. Simulations of different air change rate and different inlet/outlet heights are carried out in a residential room. And the energy consumption for cooling and the thermal comfort in the occupied zone are analyzed. According to the simulation results and the field measurements, although the air temperature is stratified in the vertical direction, this may not have an effect on thermal comfort in the occupied zone. Compared with the mixing system, the displacement ventilation may cut down 13-27% of the cooling load, and the outlet of return air set at a lower position may lead to more energy saving.