In　this　study,　an　air-refrigeration　system　for　data　center　cooling　is　proposed.　The　effects　of　pressure　ratio,　ambient　temperature,　indoor　temperature,　and　rotating　component　efficiencies　(compressor　and　expander)　on　cycle　performance　were　studied　by　numerical　simulation.　Approaches　to　improve　the　system　performance　are　proposed,　and　the　performance　of　the　composite　system　comprising　the　air-refrigeration　system　and　the　free　cooling　system　in　typical　climate　cities　is　analyzed.　The　results　show　that　the　optimal　pressure　ratio　is　1.　5　-　2.　0　in　the　actual　air-refrigeration　cycle.　The　unit　refrigeration　capacity　and　refrigeration　coefficient　of　performance　(COP)　increase　with　a　decrease　in　ambient　temperature　or　an　increase　in　indoor　temperature.　The　efficiency　of　the　expander　is　more　critical　than　that　of　the　compressor　for　improving　the　performance　of　the　air-refrigeration　system.　Under　the　optimal　pressure　ratio　of　the　actual　cycle　(both　rotating　component　efficiencies　=　0.　8),　the　refrigeration　COP　can　be　increased　by　22%　by　implementing　the　recuperator.　The　annual　energy　efficiency　ratio　(AEER)　of　the　composite　system　in　Hohhot　can　reach　14.　61,　indicating　that　it　has　more　advantages　in　areas　with　a　long　free　cooling　period　throughout　the　year.　©　2022　The　authors.