To　solve　the　problems　of　air-source　heat　pump　running　at　low　temperature　condition　that　heating　performance　is　reduced　and　the　exhaust　temperature　rises　too　fast,　the　circulation　principle　of　vapor-injected　air-source　heat　pump　system　was　proposed　by　using　injection　subcooling　and　a　R32　experimental　system　was　conducted.　The　variation　of　heat　pump　system　with　sub-cooling　mass　flow,　vapor　injection　pressure　and　evaporating　temperature　was　discussed　under　low　temperature　heating　conditions.　The　compression　system　of　the　R32　vapor-injected　heat　pump　was　also　compared　with　the　single-stage　compression　system　and　two-stage　compression　system　with　vapor　injection,　by　using　injection　subcooling.　Results　show　that　it　gets　lower　discharging　temperature.　Compared　with　the　single-stage　compression　system,　the　discharging　temperature　drops　by　28　℃　to　32　℃,　the　heating　COP　increases　by　34.4%　to　41.2%.　Compared　with　the　two-stage　compression　system　with　vapor　injection,　the　discharging　temperature　is　reduced　by　10　℃　to　18.24　℃,　whereas　the　heating　COP　is　reduced　by　3.5%　to　8.9%.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.