Driven by renewable energy, using electrocatalysis to reduce carbon dioxide (CO2) to chemicals is a key technology. It could dim global carbon emissions and promote the carbon cycle. Here, we reported an approach to prepare a Br-doped Bi nanosphere (Br-doped Bi NSP) catalyst for the preparation of formate by electrochemical conversion of CO2. The synthesized Br-doped Bi NSP catalyst manifests high selectivity toward HCOOH. At the applied potential of -0.9 V versus reversible hydrogen electrode, it could achieve a maximum FEHCOOH of 98%. It can remain constant, and the degradation is negligible in continuous electrolysis for 9 h. The excellent CO2 reduction performance is due to the electron richness at the surface of Br-doped Bi NSP induced by the electron transfer between Bi and Br. Density functional theory calculations and in situ attenuated total reflectance-Fourier transform infrared measurements were used to predict the underlying catalyst action's pathway. It can be concluded that the introduction of Br is advantageous to the *OCHO formation, which is conducive to the reduction of the determination step. This research could provide a meaningful view into anion-doping effects to enable effiective electrocatalytic material that selectively reduces carbon dioxide into valuable products.