To reduce the regeneration energy consumption of the blast furnace gas carbon capture system while rationally utilizing the waste heat of slag flushing water. This work establishes a thermodynamic model of a double absorption heat transformer. The effects of evaporation temperature, condensation temperature, absorption-evaporation temperature, and absorption temperature on system performance are investigated and analyzed. The genetic algorithm is employed for model optimization calculations, and conduct a coupling study with the blast furnace gas carbon capture system, and analyze the influence of the temperature fluctuation of the slag flushing water on the coupled system. The research results indicate that the maximum COP of the system is 0.3168 when the evaporation temperature is 75℃, 0.3032 when the condensation temperature is 20℃, 0.3116 when the absorption-evaporation temperature is 103℃, and 0.3015 when the absorption temperature is 130℃. After optimization, the heat exchange area of the system is reduced by 14.8%, and the area-to-performance ratio is improved by 16.5%. When the temperature of the slag flushing water rises from 75℃ to 85℃, the heat output of the heat pump increases by 18.6%, and the energy consumption of carbon capture decreases by approximately 10.3%. The investment payback period of the system is 3.48 years. This research broadens the application scope of double absorption heat transformer in the metallurgical industry and provides a method for the optimal design of double absorption heat transformer. It is of great significance for promoting energy conservation, emission reduction, and sustainable development in the metallurgical industry.