The　performance　characteristic　of　an　air　source　heat　pumps　(ASHP)　system　with　scroll　compressor　economizer　is　analyzed　with　thermodynamic　model.　And　the　design　parameters　and　the　key　components　of　the　cycle　are　optimized　with　discussion　of　the　predicted　results.　The　predicted　results　indicate　that　the　improved　ASHP　system　can　work　under　all　weather　conditions　and　that　this　improvement　is　conducive　to　enlarging　running　region　of　ASHP,　which　provides　an　alternative　heating　service　for　cold　areas　such　as　Northern　China.