The geometry, electronic structure and optical properties of pure and 3d transition metals-doped anatase-phase TiO2 were studied by using the plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculations show that the formation of impurity energy level is mainly contributed by 3d orbital of the transition metal doped in TiO2, and the position of impurity energy levels in the band gap is the dominating factor that decides whether the absorption threshold wavelength has a red-shift or not. The doping of Cr, Mn, Fe, Ni, Co and Cu causes the absorption wavelength to red-shift, and the absorption coefficient in the visible light region is increased; whereas the doping of Sc, Zn causes the absorption wavelength to blue-shift, but leads to higher absorption coefficients in the visible region. The doping of V not only causes the absorption wavelength to red-shift and strengthens the absorption in the ultraviolet light region, but also gives rise to extremely big absorption coefficient in the visible region.