Air　source　heat　pumps　(ASHPs)　are　widely　used　in　clean　heating　because　of　the　high　efficiency,　energy　saving　and　economic　advantages.　Efficient　defrosting　technology　for　continuous　heating　is　a　key　issue　that　must　be　addressed　when　operating　the　large　ASHP　at　low　temperatures.　To　solve　the　technical　problem,　this　paper　designed　and　built　an　experimental　ASHP　system　with　multi　outdoor　units　connected　in　parallel,　and　used　the　hot　liquid　from　the　outlet　of　the　condenser　to　defrost　outdoor　units　in　turn　to　study　the　change　of　heat　pump　per-formance　with　defrosting　start　time　at　different　outdoor　temperatures　and　outdoor　humidity,　and　compared　the　system　performance　of　the　hot　liquid　subcooling　defrosting　(HLSD)　with　that　of　the　hot　gas　bypass　defrosting　(HGBD).　The　experimental　results　showed　that　the　HLSD　enabled　the　heat　pump　to　complete　rotational　defrosting　with　good　defrosting　effect　in　the　case　of　continuous　heating.　The　lower　the　outdoor　ambient　tem-perature　and　higher　the　air　relative　humidity,　the　worse　the　heating　performance,　and　the　longer　the　defrosting　time.　When　using　the　HLSD,　the　heating　capacity　and　energy　efficiency　ratio　of　heat　pumps　could　be　increased　by　10%　to　20%　compared　with　the　HGBD.