The dependence of thermo-optic coefficients W of glasses on temperature and wavelength has been investigated. The results show that W increases linearly with temperature according to the equation Wλt = Wλo+θt, while it decreases which increasing wavelength according to the equation W2 = A0 + A1λ2 + A2λ2+A3λ-4+ …. It has been found that thermo-optic coefficients W of glasses at any temperature in the range from room temperature to annealing temperature and at any wavelength in the visible region can be calculated by these equations.