The　accurate　prediction　of　annulus　temperature　is　very　important　during　multi-gradient　pressure　control　drilling　by　the　injection　of　HGS　(hollow　glass　sphere)　in　deep　water.　In　this　paper,　the　separation　efficiency　of　HGS　under　different　influence　factors　was　studied　by　the　combination　of　new　separation　technology　and　laboratory　experiment.　Then,　considering　the　influence　of　HGS　separation　efficiency　on　mass　transfer　and　heat　transfer　process,　a　transient　wellbore　temperature　calculation　model　was　established　by　the　coupled　heat　and　mass　transfer　as　well　as　the　coupled　temperature　and　pressure　based　on　the　energy　conservation　equation,　continuity　equation　and　momentum　equation.　The　model　was　discretized　with　the　finite　difference　method　and　the　results　calculated　with　the　field　data　was　compared　the　field　measurement　data　to　verify　the　accuracy　of　the　model.　Finally,　the　sensitivity　analysis　of　the　important　factors　affecting　the　wellbore　temperature　and　thermos-physical　parameters　was　made,　such　as　separation　efficiency,　injection　rate　of　the　HGS,　position　of　the　separator　etc.　The　results　are　of　great　reference　significance　for　multi-gradient　pressure　control　drilling　in　deep　water.　©　2021,　The　Author(s),　under　exclusive　license　to　Springer　Nature　Switzerland　AG.