A　three-dimensional　mathematical　model　to　solve　the　displacement　ventilation　is　described.　The　volumetric　heat　source　method　is　adopted　for　simulate　heat　gain　and　six-flux　radiant　heat　transfer　model　is　introduced　in　the　simulation.　The　standard　k-epsilon　turbulence　model　is　used　for　predicting　indoor　air　flow　patterns,　temperature　distribution.　The　Fanger＇s　comfort　equations　are　incorporated　in　predicting　draft　risk.　The　thermal　plume　and　stratification　of　air　in　displacement　ventilation　system　are　clearly　illustrated　by　numerical　results.　The　results　indicated　the　temperature　gradient　above　the　heat　source　would　increase　with　a　higher　heat　source　location.　It　is　also　shown　that　increasing　supply　air　velocity　would　do　good　to　reduce　temperature　gradient　but　this　may　lead　to　a　higher　drat　risk　in　the　room　with　displacement　ventilation.　Thermal　discomfort　can　be　avoided　by　optimizing　the　supply　air　velocity　and　temperature.　These　results　can　be　helpful　in　better　understanding　and　designing　this　type　of　ventilation　system.