In　practical　projects,　it　is　always　observed　that　the　frosting　degree　of　two　identical　variable-frequency　air　source　heat　pumps　(VFASHPs)　in　the　same　neighborhood　varies　a　lot.　When　the　building　area　they　serve　is　smaller,　their　frosting　speed　is　slower.　This　indicates　the　relative　capacity　of　VFASHP,　i.e.　the　ratio　of　heating　capacity　of　VFASHP　at　rated　speed　to　the　space　heating　load　at　the　outdoor　design　temperature　for　heating,　has　evident　influence　on　the　frosting　suppression　performance.　However,　the　influence　mechanism　and　degree　are　unclear.　To　reveal　the　quantitative　influence　of　relative　capacity　on　its　frosting　suppression　performance,　a　mathematical　model　of　VFASHP　was　established　to　reveal　this　phenomenon　in　this　work.　By　changing　the　building　area　it　served,　the　effect　of　relative　capacities　of　VFASHP　on　frosting　suppression　performance　was　investigated　through　the　method　of　developing　frosting　maps.　Then　combining　the　meteorological　data,　its　frosting　performance　variations　in　Beijing　(low　humidity　city)　and　Xi＇an　(high　humidity　city)　were　analyzed.　Results　indicate　that　with　the　increase　of　relative　capacity,　the　frosting　suppression　performance　of　VFASHPs　can　be　enhanced　obviously.　Specifically　speaking,　the　upper　limit　temperature　of　frosting　region　of　VFASHP　decreases,　while　the　critical　relative　humidity　for　frosting　increases.　Consequently,　when　the　relative　capacity　increases　by　10%-50%,　the　frosting　duration　in　Beijing　decreases　by　3.29%-19.63%.　Compared　with　that　in　Beijing,　the　decrease　rate　of　frosting　duration　in　Xi＇an　is　0.30%-3.07%　greater.