In　this　paper,　the　thermal　performance　of　a　radiant　floor　heating/cooling　system　for　an　office　building　in　Beijing　had　been　researched.　Through　experimental　method,　condensation　condition　on　the　floor　surface　in　summer　cooling　condition　and　influences　of　floor　surface　temperature　on　mean　radiant　temperature,　operative　temperature　and　vertical　air　temperature　differences　were　mainly　investigated.　The　experimental　results　show　that:　1)　when　supply　water　temperature　of　the　radiant　floor　cooling　system　is　controlled　above　16.5　degrees　C　and　the　fan　coil　unit　operates　at　a　low　air　velocity,　condensation　on　the　floor　surface　can　be　prevented.　The　indoor　thermal　comfort　is　satisfied.　2)　In　the　radiant　floor　cooling　system,　indoor　mean　radiant　temperature　and　operative　temperature　are　lower　2　degrees　C　and　1　degrees　C　than　air　temperature　respectively.　The　vertical　air　temperature　difference　is　about　1.7　similar　to　3.7　degrees　C　from　0.1　m　to　1.1　m　above　the　floor.　The　cooling　capacity　of　the　radiant　floor　heat　exchanger　is　about　30-60W/m(2).