Highly selective electrocatalytic reduction of CO2 to formate is considered a valid route for alleviating the continuing increase in atmospheric CO2 concentration. Herein, Indium-doped Bi/Bi2O3 (In-Bi/Bi2O3) electrocatalyst grown in situ on carbon paper (CP) was obtained via a relatively simple one-step solvothermal synthesis method and utilized in CO2 reduction reaction (CO2RR) for formate production. The In-Bi/Bi2O3/CP exhibits superior Faradaic Efficiency for formate, i.e., FEformate = 96.3 %, and a partial current density of 6.74 mA cm−2 at −1.6 V (vs Ag/AgCl) in the H-type cell. Furthermore, FEformate of the electrode remains consistently above 90 % within long-term stability testing (60 h). By density functional theory (DFT) calculations, it is found that incorporating In into Bi/Bi2O3 can generate more active sites and facilitate the preferential adsorption of *OOCH intermediates, alleviating competitive adsorption of *H during CO2 reduction reaction (CO2RR), thereby accelerating formate production.