To date, the electrochemical reduction of CO₂ (CO₂RR) into valuable chemicals is a promising method for combating global warming. However, finding a suitable electrocatalyst for CO₂RR is critical to reducing CO₂ emissions. Herein, the CO₂RR mechanism on a pristine monoclinic Bi₂O₃ (120) surface was thoroughly investigated using density-functional theory (DFT) calculations. The CO₂ adsorption modes of side-on, end-on, and chemisorbed were compared, with the chemisorbed species outperforming for CO₂ activation. Furthermore, analyses of the Bader charge, the density of states, and electron density difference strongly suggest that the Bi₂O₃ (120) surface has excellent activation for CO₂ molecules. More importantly, the DFT calculations revealed that the electrochemical CO₂RR over the Bi₂O₃ surface favors both formic acid and methanol in the limiting-potential step of *CO₂ $\to$ *COOH with the free energy barriers of 0.86 eV and 0.87 eV with and without solvent, respectively. The microkinetic simulation also supports the DFT result, showing the possibility of more selective production by predicting desorption temperatures. This research suggests a promising way for CO₂RR mechanisms on pristine monoclinic Bi₂O₃ surfaces to produce formic acid (HCOOH) and methanol (CH₃OH).