The invention relates to a low-cost and high-efficiency absorption-desorption decoupling method for contaminant-CO2 synergistic capture. According to the method, an optimization model of absorption-desorption decoupling control for contaminant-CO2 synergistic capture under different working conditions is built, the optimization objective is to obtain high-purity liquid contaminants and CO2 at low cost and efficiently, and an adaptive penalty function is constructed to transform a solution of a constrained optimization problem into that of an unconstrained optimization problem, thereby controlling parameters in a real-time, precise and stable manner. Moreover, supported by means of flue gas pre-scrubbing and cooling, multi-stage intercooling and column-top demisting, the method of the present invention achieves efficient capture of contaminants and CO2. According to the invention, the absorption process is decoupled from the desorption process, and the coordinated control of temperature-pH-liquid-gas ratio and rich liquid flow-desorption temperature in all cycles is carried out to realize the synergistic capture-regeneration-concentration of contaminants and CO2 with high efficiency and low energy consumption, thereby reducing the high cost of the traditional method where a flue gas cleaning system and a carbon capture system operate separately.