In　this　paper,　a　three-dimensional　numerical　heat　transfer　model　of　the　vertical　U-tube　is　established　using　FLUENT　software　to　research　on　its　unsteady　fluid-structure　heat　transfer　process　in　order　to　better　simulate　the　heat　transfer　area　of　the　underground　pipes　in　ground　source　heat　pump　system.　In　winter,　the　simulation　results　coincide　with　the　experimental　dates.　In　addition,　this　paper　also　analyzes　the　effects　of　the　flow　rate　within　the　pipe,　the　thermal　conductivity　of　grout,　the　shank　spacing　of　U-tube　and　the　borehole　depth　on　the　heat　transfer　rate.　The　simulation　results　show　that　the　heat　transfer　of　underground　pipe　per　meter　is　proportional　to　the　flow　rate　within　the　pipe,　the　thermal　conductivity　of　grout　and　the　shank　spacing　of　U-tube,　while　it　has　an　inverse　relationship　with　the　borehole　depth.