In order to verify the resource utilization of CO2 from coal-fired flue gas, the conversion of CO2 by sodium borohydride was investigated under atmospheric pressure and moderate temperature. According to the product analysis results of mass spectrometry and ion chromatography, combined with the comparison of electrode potentials, the mechanism of CO2 reaction with sodium borohydride was deduced, in which formate was confirmed as the main reduction product, and the intermediates of [BHi(HCO2)(OH)(3-i)](-1) were considered as the essential mediums for the formation of formate. The feasibility of this conversion was studied thermodynamically.