The flue gas of the natural gas-fired boiler contains a large number of sensible heat and latent heat, and make full use of the heat can reduce the energy consumption and achieve the emission reduction. In recent years, with the absorption heat exchange technology becomes more and more mature, the absorption heat exchange technology can realize the flue gas waste heat recovery deeply. It uses a heat pump to produce a low temperature environment, extracting heat from the flue gas, more thoroughly, because the water vapor is condensed, the chimney is not white smoke, energy saving and environmental protection effect is more significant, the technology gradually obtained the industry recognition and attention. This paper introduces the flue gas waste heat recovery system based on absorption heat exchange, the purification effect of flue gas condensation were tested, and the discharge of the system was analyzed and evaluated, it provides an important reference for the popularization and application of the system.