This　paper　presents　a　novel　air　source　heat　pump　for　heating　of　buildings　named　air　source　heat　pump　with　multiple　parallel　outdoor　units　(ASHPMO).　Multiple　outdoor　units　were　connected　in　parallel　with　the　aim　of　realising　alternate　defrosting　and　uninterrupted　heating　simultaneously.　An　experimental　apparatus　of　the　ASHPMO　system　was　developed.　The　defrosting　performance　was　experimentally　investigated　under　different　outdoor　air　temperatures,　outdoor　air　relative　humidity,　and　condensation　temperatures,　among　other　factors.　The　test　results　showed　that　the　novel　ASHPMO　system　could　provide　continuous　heating　when　defrosting　even　under　an　outdoor　air　temperature　of　-10　degrees　C.　Variations　in　compressor　vapour　suction　and　discharge　pressure　and　temperature　were　observed.　The　minimum　heating　capacity　could　still　reach　60%　of　that　without　defrosting.　Under　the　defrosting　condition　with　outdoor　air　temperature　-10　degrees　C,　both　the　heating　coefficient　of　performance　(heating　COP)　and　total　energy　efficiency　ratio　(EER)　of　the　system　can　reach　to　2.0　and　2.32,　respectively.