Using renewable electrical energy to convert carbon dioxide to high-value chemicals and fuels holds significant importance for mitigating the greenhouse gas effect and achieving carbon neutrality. In this research, we developed a simple and effective method for preparing P-doped In_2O_3 nanoparticles and applied them in the electrocatalytic reduction of CO_2 to formate. For example, the P-doped In_2O_3 catalyst exhibited 88.2% faradaic eficieney for formate production at -1.45 V vs. RHE in an H-type electrolysis cell, demonstrating excellent stability. Further experimental analysis and theoretical studies indicated that incorporating P elements into the In_2O_3 lattice significantly enhanced both the ad.sorption and activation of CO_2 molecules. Additionally, it reduced the Gibbs free energy for the formation of *HCOO intermediates and strengthened the adsorption of *HCOO, ultimately promoting formate generation. This study elucidates the inherent mechanisms of non-metallic P doping in enhancing the performance of CO_2 reduction reactions and provides a viable strategy for the design of high-performance electrocatalysts based on metal oxides for future applications.