Vapor　injection　with　flash　tank　has　proven　to　be　effective　in　improving　the　performance　of　vapor　compression　heat　pumps　at　low　temperatures.　However,　the　benefit　of　vapor　injection　would　be　reduced　when　zeotropic　mixtures　are　used,　due　to　the　loss　of　low-boiling　component,　causing　by　the　vapor-liquid　separation　in　flash　tank.　Hence,　a　novel　vapor　injection　cycle　(HFCC)　using　a　cascade　condenser　to　liquefy　the　separated　vapor　stream　for　evaporation　was　proposed　in　this　paper.　The　amount　and　state　of　the　injected　stream　was　controlled　via　a　branch　circuit.　The　performances　of　the　HFCC　system　were　investigated　and　compared　with　the　flash　tank　cycle　(FTC)　and　the　hybrid　cycle　(HFIC),　based　on　the　developed　mathematical　model.　Simulation　results　based　on　R290/R600a　(50/50)　indicated　that　the　HFCC　had　1.9%　and　2.6%　improvement　in　COP　compared　with　that　of　the　HFIC　and　FTC,　respectively,　under　the　same　conditions.　HFCC　became　more　superior　to　FTC　in　terms　of　COP　as　the　cycle　temperature　lift　increases,　by　either　decreasing　evaporation　temperature　or　increasing　condensation　temperature.　The　COP　improvement　of　HFCC　depended　largely　on　the　circulating　composition.　Generally,　zeotropic　mixtures　with　large　temperature　glides　showed　higher　COP　improvement　in　comparison　with　FTC.