Abstract: In order to expand the range of bandgap value tuning for monolayer Bi₂O₂S, a systematic study of the material structure and electronic properties of monolayer Bi₂O₂S with halogen element Y (Y = F, Cl, Br, I) passivation on its surface was conducted using first-principles calculation methods. The band structures of Bi₂O₂S—Y (Y = F, Cl, Br, I) were calculated using the generalized gradient approximation (GGA-PBE) and the hybrid density functional (HSE06) , and the results obtained from different basis set functionals were compared.It is found that when the surface is passivated with different terminal atoms such as F, Cl, Br, and I, the structure of monolayer Bi₂O₂S remains almost unchanged. The F, Cl and Br atoms tend to obtain electrons from the bare Bi₂O₂S layer while the I terminations tend to lose electrons. The passivated monolayer Bi₂O₂S shows an indirect band gap that can be adjusted over a wide range (1.249 eV~1.996 eV), depending on the type of halogen element used for surface passivation Y. The research indicates that passivation with halogen elements on the surface can effectively modulate the bandgap of two-dimensional Bi₂O₂S, which holds certain guiding significant for its application in the field of optoelectronics.