The　heat　pump　system　with　scroll　compressor　flash-tank　is　presented,　and　it　was　compared　with　sub-cooler　sys　tem　in　structural　characteristics.　The　experimental　study　and　performance　analyses　of　the　heat　pump　prototype　were　implemented,　and　the　results　showed　that　the　heating　capacity　of　the　prototype　decreased　along　with　lowering　the　evaporating　temperature,　but　the　decreasing　rate　is　much　slower　than　that　of　conventional　air　source　heat　pump　system.　The　electric　power　input　increased　a　little　at　the　same　time.　The　heat　pump　system　with　flash-tank　can　improve　the　heating　performances　more　efficiently　than　the　system　with　sub-cooler　under　low　ambient　temperature　conditions,　so　it　is　much　suitable　to　the　small　air　source　heat　pump　used　in　cold　area.