The　environment　and　energy　performance　of　an　actual　coupled　earth　tube　and　natural　ventilation　system　in　a　gymnasium　was　measured　during　the　post-acceptance　step　in　winter　and　summer　at　natural　ventilation　states.　Since　the　measurement　result　at　design　weather　condition　has　not　been　obtained,　the　authors　calculated　the　natural　ventilation　air　volume　and　the　indoor　temperature　in　winter,　summer　and　intermediate　season　at　a　windless　state　by　the　use　of　CFD　(Computational　Fluid　Dynamics)　coupled　analysis　method　with　natural　ventilation.