Abstract: To investigate the mechanism of NO₂ sensing enhancement, the density functional theory was used to study the adsorption behavior of NO₂ molecule on the surface of indium-doped SnO₂(110). Theoretical calculations showed that a new electronic state appeared near the Fermi level after indium doping, which increased the conductivity of SnO₂, promoted the formation of SnO₂(110) defect surface with vacancies and facilitated the pre-adsorption process of active oxygen on the surface. Indium doping may significantly improve the adsorption of NO₂ onto the surface. The increased selectivity and sensitivity of NO₂ gas is mainly ascribed to the formation of defect surface with oxygen vacancies after indium doping. Moreover, the pre-adsorption of oxygen depends on the specific adsorption sites. The NO₂ molecule located at the Sn_5c site of the surface gains charges from the surface, generating oxygen vacancies. That is why indium-doped SnO₂(110) exhibits excellent performance of NO₂ gas-sensitive adsorption.