Abstract: The flue gas discharged by conventional natural gas boilers contains a large amount of water vapor, which cannot effectively recover the latent heat of water vapor condensation because of its failure to reduce the flue gas below the dew point temperature. In this study, an electric heat pump with mixed working medium HD-01 and a wall heat exchanger were used to recover the waste heat from flue gas of a natural gas boiler. An experimental platform for deep recovery of flue gas waste heat was also built, and a theoretical model for deep recovery of flue gas waste heat was improved based on the experimental results. The experimental results show that the average exhaust temperature of the system is 33.1℃, and the whitening effect of smoke is obvious. The system can increase the temperature of heat network backwater from 42.9℃ to 60.0℃ on average, and the actual waste heat recovery power accounts for 8.7% of the average boiler power, and the average COP is about 5.4.The economic analysis shows that the waste heat recovery cost of the system is about 195, 000 yuan, which can save 87, 746.44 yuan per year, and the investment recovery period is 2.2 years. The heating cost of the system is nearly 49.0% less than that of natural gas boilers.