The invention discloses a microbial electrolysis cell integrating functions of CO2 conversion and sewage treatment, which comprises a microbial electrolysis cell shell, the inside of the microbial electrolysis cell shell is provided with an anion / cation exchange membrane for dividing the microbial electrolysis cell shell into an anode chamber and a cathode chamber, the insides of the anode chamber and the cathode chamber for accommodating to-be-treated sewage are respectively provided with an anode and a cathode which are connected with an external power supply, the inside of the cathode chamber is also provided with a reference electrode for controlling the electric potential of the cathode, the upper end of the cathode chamber is provided with a cathode product outlet, and the anode chamber is communicated with the cathode chamber by an air-guide tube. In the invention, sewage is fed into the anode chamber and used as a nutrient source for the growth of various microbes, and at room temperature, the microbes carry out catabolism on organic matters in the sewage so as to achieve a wastewater treatment process. In the CO2 capturing and conversion process, CO2 released by the anode is fed into the cathode chamber by the air-guide tube, then under the catalytic action of bacteria in the cathode chamber, an effect of CO2 capturing and an effect of converting the CO2 into CH4 are achieved.