The coherent potential method has been applied for the investigation of Co substitutional doping influence on the spectral and magnetic properties of TiO2 rutile (100) surface. Both stoichiometric and nonstoichiometric oxygen compositions have been considered. For the stoichiometric case, the energy spectrum corresponds to half-metallic ferromagnet. The Co ions are in 2 + formal oxidation state with a spin magnetic moment of 0.8 μB. The presence of oxygen vacancies makes the surface insulating and increases the Co spin magnetic moment value.