Air　source　heat　pumps　(ASHPs)　have　been　widely　used　for　space　heating　in　cold　winter.　When　it　operates　in　frosting　environment,　defrosting　is　necessary　to　maintain　the　system　performance　resulting　in　a　discontinuous　space　heating.　The　defrosting　time　is　an　important　parameter　to　evaluate　the　performance　of　different　defrosting　methods.　At　present,　the　widely　applied　ways　for　defrosting　are　the　standard　reverse-cycle　defrosting　and　hot-gas　bypass　defrosting　methods.　For　the　two　defrosting　methods,　the　biggest　problem　is　that　no　heat　source　is　available　for　the　defrosting　cycle　which　leads　to　a　long　defrosting　time.　For　the　past　few　years,　study　on　the　use　of　heat　exchangers　with　phase　change　material　(PCM-HE)　to　storage　heat　for　the　defrosting　receives　lots　interest.　This　paper　presents　a　review　of　these　reported　defrosting　methods　using　PCM-HE.　The　ASHPs　with　PCM-HE　and　their　defrosting　principles　are　introduced.　Furthermore,　the　frequently-used　phase　change　materials　together　with　structure　of　PCM-HE　are　also　summarized.　Finally,　the　further　research　direction　to　realize　effective　defrosting　and　continuous　heating　of　air-source　heat　pump　products　is　discussed.　(C)　2019　The　Authors.　Published　by　Elsevier　Ltd.