Abstract: A new configuration of dual-pressure condensation heat pump water heater system（DPS）is proposed,and hydrocarbon（HC）zeotropic working medium is used as refrigerant. Therefore,the water is heated continously step by step with low exergy destruction in the condenser. Then,the thermal performance of the system is optimized by golden section method. The results indicate that the thermodynamic with pure refrigerant. The dual-pressure condensation system obtains the maximum coefficient of performance（COP）at the optimal intermediate water temperature. Under the normal working condition of the heat pump water heater,the COP of DPS system using R600/R601a（40/60）is as high as 5.17,which is 9.45% and 14.25% higher than that of DPS system and the singlestage system with pure refrigerant,respectively. When non-zeotropic working medium with suitable temperature glide is used,the exergy destruction can be significantly reduced to improve thermal matching of the condenser,the exergy efficiency of the overall system is enhanced by up to 11.70%. Consequently,it is recommended that R600/R601a（40/60）is the best candidate for water heater heat pump under normal working condition.