Abstract: Titanium dioxide (TiO2¬) is a widely used material with many industrial applications. Because of the photocatalytic activity and environmental compatibility, it has tremendous potential applications in solar cells, dye industries, electronic devices, sensors and transformers. Density functional - pseudopotential calculations were performed to study the effect of hydrogen doping in bulk, and also H-doping and oxygen vacancy on electronic structure and stability of (001) surface of TiO2 in the anatase phase. In the framework of ab-initio atomistic thermodynamic, we argue that the anatase TiO2 prefers a defected oxygen layer termination in the (001) direction. The obtained electronic structures indicate that deep hydrogen doping in this stable termination creates a mid-gap state about 0.52 eV below the conduction band and hence decreases the band gap of the system. This phenomenon may explain the enhanced photocatalytic activity of the anatase TiO2 (001) surface after hydrogenation.