Abstract: By the limit of heat source temperature as well as system performance，outlet water temperature of single-stage vapour-compression is generally around 50℃.No way to be satisfied with the occasions in which large temperature difference is requested does this heat pump have.Large temperature difference can be achieved by auto-cascade heat pump system.Data computation and thermal energy performance analysis are carried on this cycle system，on the basis of the design of the system and the choice suits the system operation in non-azeotropic mixture foundation.Theoretical analysis shows that the suction and exhaust pressure will increase with R134a filling concentration charges.A maximum value of COP and a minimum value of pressure ratio appear with the increase of the concentration.Linear relationship of the exhaust pressure and the filling concentration，basically，is assumed condensing the lowest minimum and vaporization temperature is certain.