The　influence　of　expander　performance　on　compressed　air　energy　storage　(CAES)　system　has　been　widely　studied.　However,　only　a　few　researches　focus　on　the　effect　of　irreversible　loss,　and　especially　the　influence　of　pressure　loss　on　expander　performance　is　often　neglected.　The　addition　of　lubrication　oil　has　a　marked　influence　on　the　pressure　loss.　To　clarify　the　influence　of　the　lubrication　oil　on　pressure　loss　of　single　screw　expander　(SSE),　a　comparative　experiment　was　undertaken　to　investigate　six　different　viscosity　lubrication　oils　(10#,　22#,　32#,　46#,　68#,　and　80#)　under　different　operating　conditions.　Results　show　that　pressure　loss,　proportion　(∆pin,　∆pout,　PLRin,　and　PLRout),　and　pressure　energy　loss　influence　rate　of　shaft　efficiency　(PELRe)　can　be　significantly　reduced　by　increasing　kinematic　viscosity　of　lubrication　oil.　In　contrast,　although　the　shaft　efficiency　can　be　effectively　improved　to　a　certain　extent　by　increasing　kinematic　viscosity　of　lubrication　oil,　there　is　no　positive　relationship　between　them.　©　2024　Beijing　University　of　Technology.　All　rights　reserved.