We report the anatase titanium dioxide(101) surface adsorption of sp~3-hybridized gas molecules,including NH_3,H_2O and CH_4,using first-principles plane-wave ultrasoft pseudopotential based on the density functional theory.The results show that it is much easier for a surface with oxygen vacancies to adsorb gas molecules than it is for a surface without oxygen vacancies.The main factor affecting adsorption stability and energy is the polarizability of molecules,and adsorption is induced by surface oxygen vacancies of the negatively charged center.The analyses of state densities and charge population show that charge transfer occurs at the molecule surface upon adsorption and that the number of transferred charge reduces in the order of N,O and C.Moreover,the adsorption method is chemical adsorption,and adsorption stability decreases in the order of NH_3,H_2O and CH_4.Analyses of absorption and reflectance spectra reveal that after absorbed CH_4 and H_2O,compared with the surface with oxygen vacancy,the optical properties of materials surface,including its absorption coefficients and reflectivity index,have slight changes,however,absorption coefficient and reflectivity would greatly increase after NH_3 adsorption.These findings illustrate that anatase titanium dioxide(101) surface is extremely sensitive to NH_3. We report the anatase titanium dioxide (101) surface adsorption of sp ~ 3-hybridized gas molecules, including NH_3, H_2O and CH_4, using first-principles plane-wave ultrasoft pseudopotential based on the density functional theory. The results show that it is much easier for a surface with oxygen vacancies to adsorb gas molecules than it is for surface without oxygen vacancies. the main factor affect adsorption stability and energy is the polarizability of molecules, and adsorption is induced by surface oxygen vacancies of the negatively charged center. analyzes of state densities and charge population show that charge transfer occurs at the molecule surface upon adsorption and that the number of transferred charge reduces in the order of N, O and C. Moreover, the adsorption method is chemical adsorption, and adsorption stability decreases in the order of NH_3, H_2O and CH_4.Analyses of absorption and reflectance spectra reveal that after absorbed CH_4 and H_2O, compared with the surface with oxygen vacancy, the optical properties of materials surface, including its absorption coefficients and reflectivity index, have slight changes changes, however, absorption coefficient and reflectivity would greatly boost after NH3 adsorption.These findings illustrate that anatase titanium dioxide (101) surface is extremely sensitive to NH_3.