The conversion of CO₂ into high value-added chemicals is an effective way to realize the carbon cycle, alleviate energy crisis and environmental problems. The preparation of metal-semiconductor electrodes provides a new idea for CO₂ conversion by photoelectric coupling technology. In this study, Si was etched in alkali solution, on which a bimetallic Bi, Zn co-modified Si photoelectrocathode (BiZn_x/Si) was prepared via the electrodeposition process, for the photoelectrochemical reduction CO₂. The results show that the introduction of Bi and Zn can improve the light absorption performance, reduce the electrochemical impedance, and increase the electrochemical active surface area (ECSA). Especially, the ECSA of the best photoelectrocathode BiZn₂/Si is 0.15 mF·cm^-2. Besides, the cooperative effect of Bi and Zn can improve the adsorption performance toward the intermediates *OCHO. During the photoelectrochemical reduction of CO₂, the Faradaic efficiency for HCOOH reaches up to 96.1% on the best photoelectrocathode BiZn₂/Si at the potential of -0.8 V (vs. RHE). Moreover, the photocurrent intensity on the photoelectrocathode BiZn₂/Si remained -13 mA·cm^-2 during the 10 h photoelectric stability test, suggesting its high stability.