Medium-deep　borehole　heat　exchanger　(MDBHE)　has　attracted　considerable　attention　because　of　its　ability　to　acquire　large　quantities　of　geothermal　energy.　Geological　conditions　in　the　medium-deep　reservoir　significantly　affect　thermal　extraction.　This　study　proposes　a　transient　heat　transfer　model　for　MDBHE;　the　accuracy　of　the　model　is　validated　using　experimental　data.　Using　this　model,　the　thermal　performance　of　MDBHE　under　different　geological　parameters　is　investigated　based　on　the　operation　characteristics　of　MDBHE.　Sensitive　analysis　highlights　the　importance　of　the　effects　of　geothermal　gradient,　thermal　conductivity,　and　heat　capacity　of　the　rock　soil　on　thermal　extraction　load　(TEL)　and　thermal　effect　radius　(TER)　of　the　MDBHE.　Results　indicate　that　geothermal　gradient　affects　the　TEL　mostly　and　heat　capacity　has　the　greatest　impact　on　TER.　In　regions　with　low　rock-soil　heat　capacity,　borehole　spacing　should　be　sufficiently　wide　to　prevent　thermal　interference　between　adjacent　boreholes.　For　continuous　operations　of　MDBHE,　the　annual　average　TEL　declines　with　operating　year　and　the　declining　proportion　is　the　largest　in　the　second　year　for　4%–6%.　Besides,　the　maximum　TER　increases,　with　maximal　increasing　proportion　in　the　second　year　up　to　∼80%.　Under　different　geological　parameters,　the　declining　proportion　of　TEL　and　increasing　proportion　of　TER　within　the　same　year　are　almost　identical.　In　addition,　the　thermal　performance　of　MDBHE　under　layered　subsurface　is　presented.　Layered　RTCs　and　geothermal　gradients　have　a　significant　effect　on　the　TEL　of　MDBHE;　and　layered　subsurface　with　segmented　RTCs　and　rock-soil　heat　capacities　considerably　affects　the　TER.　This　study　will　enable　the　wide　promotion　of　MDBHE　application　in　different　regions.　©　2019　Elsevier　Ltd