In　this　paper,　an　air　source　heat　pump　water　heater　based　on　a　dual　cylinder　compressor　(DCWH)　with　constant　speed　is　proposed,　a　mathematical　model　is　established　and　a　test　bench　for　the　new　heat　pump　water　heater　is　built.　Three　different　operating　modes:　DSP　(Double　stage　parallel　mode),　SS　(Single　stage　compression　mode),　and　DSS　(Double　stage　series　mode)　are　developed,　and　the　working　performance　of　it　is　compared　with　the　conventional　variable　frequency　compressor　water　heater　(VFWH).　The　results　show　that　the　optimal　volumetric　ratio　of　the　dual　cylinder　compressor　is　0.6,　0.56,　and　0.5,　respectively.　The　DCWH　system　can　effectively　reduce　the　discharge　temperature　and　pressure.　Compared　with　the　VFWH　system,　the　heating　time　of　hot　water　can　be　reduced　by　20.27　%,　and　the　water　heater　system　can　run　under　ambient　temperature　lower　than　-18　degrees　C.　The　hot　water　production　capacity　increase　26　%,　energy　efficiency　ratio　is　about　6.7-8.4　%　higher　than　that　of　the　VFWH　system.