CO2　air-source　heat　pump　is　regarded　as　a　promising　technology　for　domestic　hot　water　and　automotive　air-conditioning　system.　However,　its　coefficient　of　performance　is　not　very　satisfactory　when　it　is　used　for　space　heating　in　winter,　while　this　phenomenon　is　more　obvious　at　the　condition　of　taking　conventional　radiator　as　a　heating　terminal　unit.　To　cope　with　this　issue,　a　transcritical　CO2　air-source　heat　pump　system　combined　with　the　terminal　of　radiator　and　floor　radiant　coil　for　space　heating　was　developed　in　this　paper,　for　fulfilling　the　energy　cascade　utilization.　The　performance　and　feasibility　of　the　studied　system　were　investigated　using　Transient　System　Simulation　Program　and　compared　with　a　benchmark　system　in　five　locations　with　different　climate　zones,　China.　The　results　showed　that,　taken　Shenyang　as　an　example,　the　inlet　water　temperature　of　heat　pump　unit　of　the　studied　system　and　the　benchmark　system　were　36　°C　and　50　°C　respectively.　Also　the　average　coefficient　of　performance　and　heating　seasonal　performance　factor　of　CO2　air-source　heat　pump　unit　were　17%–28%　and　9%–22%　higher,　respectively,　compared　with　the　benchmark　system　during　the　entire　heating　period.　This　study　is　helpful　to　improve　the　application　of　transcritical　CO2　air-source　heat　pump　for　space　heating　in　severe　and　cold　zones　in　China.　©　2021