The invention relates to a method and a system for acquiring CO2 by temperature-lowering absorption and low-voltage desorption, in particular to a method and a system for captauring CO2 by a method of absorption and desorption, which overcomes the defects of difficult control, large energy consumption of the warming voltage-varying desorption method adopted by power plants to capturing CO2 and the defects of toxic and hazardous gas generated during capturing CO2 by chemisorption method. The method comprises temperature reduction by flue gases, communicating absorption of a first absorption and desorption tower, communicating absorption of a second absorption and desorption tower, and electrified temperature-increasing desorption, purification and temperature reduction of the first the absorption and desorption tower, CO2 gas purging, electrified temperature-increasing desorption, purification and temperature reduction of the second absorption and desorption tower, and communicating absorption of the first the absorption and desorption tower during a next absorption and desorption circulating process. In the system, the first and the second absorption and desorption towers are connected with an alternating current power supply through a first switch and a second switch, and the alternating current power supply is connected with the first and the second absorption and desorption towers. In the utility model, a physical adsorption method is adopted, thereby avoiding the generation of other toxic and hazardous gases by chemical methods. The method and the system are used for capturing CO2 in flue gases in coal industry works and power plants.