The electronic structure and optical properties of SnO2 (110) / FAPbBrI2 (001) interface were studied using first- principles based on density functional theory (DFT). FAPbBrI2 is a direct bandgap semiconductor material with a bandgap value of 1. 58 eV. By constructing a model of the interface between SnO2 (110) and FAPbBrI2 (001), the lattice mismatch is found to be 4. 28% , and the interface binding energy is - 0. 116 eV/ ?2 , indicating the stability of this interface structure. Through the analysis of the density of states (DOS) of SnO2 (110) / FAPbBrI2 (001) interface, it was discovered that interface states primarily originated from hybridization of O 2p, I 5p, Br 4p, and Pb 6p orbital electrons at the interface. Charge density difference and Bader charge analysis reveal significant charge transfer at the interface, promoting bonding between the interface atoms and enhancing interface stability. And effective charge separation led to a significant improvement in the absorption coefficient of the SnO2 (110) / FAPbBrI2 (001) interface compared to the surfaces of SnO2 (110) and FAPbBrI2 (001).