Deep　borehole　ground　source　heat　pump(DB-GSHP)　is　a　type　of　heating　system　which　extracts　the　deep　geothermal.　This　paper　tested　outlet　temperature,　heat　transfer　capacity　and　COP　of　DB-GSHP　on　a　demonstrative　project,　which　showed　that　outlet　temperature　and　heat　transfer　capacity　of　borehole　heat　exchanger　was　at　26.9　and　284.2　kW　respectively.　The　COP　of　average　heating　unit　was　6.4　and　COP　of　average　heating　system　was　4.7.　The　numerical　model　of　deep　borehole　heat　exchanger　was　proposed　to　optimize　tube　structure　on　pipe　diameter　and　insulation　layer　length.　With　the　outer　pipe　diameter　increasing,　outlet　temperature　and　heat　capacity　increase　by　11.38%　and　32.3%,　respectively,　while　outlet　temperature　and　heat　capacity　decrease　by　7.35%　and　15.67%　with　the　inner　pipe　diameter　increasing.　The　comparison　demonstrated　that　larger　outer　pipe　diameter　and　smaller　inner　pipe　diameter　benefits　the　heat　transfer.　Laying　insulation　layer　on　inner　pipe　can　reduce　heat　transfer　loss　effectively.　However,　the　heat　transfer　loss　will　be　unobvious　at　high　flow　rate.　The　results　are　of　great　significance　to　the　promotion　of　DB-GSHP　and　the　design　for　deep　borehole　heat　exchanger.　©　2019,　Science　Press.　All　right　reserved.