The invention provides an electroreduction CO2 device. The electroreduction CO2 device comprises an electrochemical reaction unit and a cathode feeding unit, wherein the electrochemical reaction unitcomprises a cathode chamber, an anode chamber and a membrane electrode, and a diaphragm of the membrane electrode is an anion-exchange membrane; and the cathode feeding unit is connected with a feeding opening of the cathode chamber, and the cathode feeding unit inputs humidified gas containing CO2 to the cathode chamber. The invention further provides an electroreduction CO2 method. The electroreduction CO2 device and method have the advantages of simple and convenient technology, green and environmental protection, low equipment requirement, low manufacturing cost and the like, are very suitable for industrial synthesis gas production, and good economic benefits and social benefits can be achieved.