The invention belongs to the technical field of chemical engineering and particularly relates to a device and a method for capturing and converting CO2 from a mixed gas containing CO2. In the device, the mixed gas containing CO2 sequentially passes through an absorption device (1) and a desorption device (2) to obtain relatively pure CO2 gas, CO2 gas enters a reaction device (3) which is filled with ionic liquid-immobilized solid catalyst and is reacted with epoxide to generate cyclic carbonate, the reaction products are extracted from the bottom of the rector, unreacted CO2 gas and epoxide are extracted from the top of the reactor, enter a separation device for gas separation and finally return to the reaction device and are reused again. By the device, CO2 in natural gas, synthetic gas and flue gas is removed and meanwhile the collected CO2 can be fully utilized to synthesize cyclic carbonates.