The invention belongs to the technical field of coal-fired power plant CO2 capture, and discloses a system and a method for capturing coal-fired power plant CO2 by using a mixed conduction membrane. The system comprises a coal-fired power plant boiler, a water vapor-methane reformer, a mixed conduction membrane MECC, a mixer, a heat exchanger, a waste heat boiler, a condenser, a multi-stage compressor, a steam turbine, a power generator and the like. According to the invention, a CO2 capture process with high operation flexibility is adopted, wherein gas discharged by a coal-fired power plantboiler and air are mixed and introduced into the feeding side of the mixed conduction membrane, the gas discharged by the permeation side of the mixed conduction membrane contains high-concentration CO2 by using the electrochemical reaction on the feeding side of the mixed conduction membrane, and the O2 in the discharged gas and the CO and H2 discharged by the reformer are subjected to an oxidation reaction to generate CO2 and H2O, such that the CO2 emission of the coal-fired power plant is greatly reduced; the generated steam enters the steam turbine to do work so as to perform waste heat recovery and utilization; and with the system and the method, the coal-fired power plant CO2 emission reduction and the low-energy consumption recovery of CO2 are achieved so as to achieve the purposesof low energy consumption and high efficiency.