To　solve　the　problem　of　reverse-cycle　defrosting　of　large　and　medium　air　source　heat　pump,　a　new　type　of　air　source　heat　pump　cycle　with　multiple　parallel　outdoor　machines　defrosting　alternatively　was　proposed.　By　switching　valves　to　realize　an　outdoor　machine　defrosting,　the　rest　of　the　outdoor　machines　were　in　the　state　of　normal　evaporative　heat　absorption　at　the　same　time.　In　the　case　of　non-stopping　heating,　defrosting　can　be　realized　while　recovering　frost　thawing　cooling　capacity.　A　test　platform　of　research　system　was　built　in　an　artificial　environment　room.　The　law　of　the　variation　of　the　compressor　suction,　exhaust　pressure　and　the　system　thermal　performance　in　the　condition　of　frost　free,　frosting　and　defrosting　were　discussed.　©　2019,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.