The　ground　heat　exchanger　is　an　important　component　of　the　ground　coupled　heat　pump　(GCHP)　and　the　U-tube　is　most　commonly　used　ground　heat　exchanger.　The　heat　transfer　between　the　U-tube　and　the　soil　is　affected　by　many　factors.　To　analyze　the　influence　of　these　factors　on　the　heat　transfer　of　the　U-tube,　this　paper　built　a　full　scale　3D　numerical　model　of　a　U-tube　ground　heat　exchanger　of　a　ground　coupled　heat　pump　(GCHP).　Then　numerical　studies　on　the　influence　of　various　factors　such　as　U-tube　depth,　inlet　temperature,　fluid　velocity　on　the　heat　transfer　of　the　U-tube　were　carried　out　using　CFD　software　FLUENT.　The　computed　influence　on　the　heat　transfer　can　provide　some　insight　to　the　optimization　design.