Wavelength dependence of the electro-optic overlap integral factor (Γ) for a single-mode LiNbO3 (LN) channel waveguide was analyzed experimentally and theoretically. By measuring the half-wave voltage (Vπ) of the LN waveguide at different wavelengths and then substituting the measured values into a formula that describes the relationship between Vπ and Γ, the quantitative dependence of Γ on wavelength was obtained; and it showed that Γ rapidly decreases with increasing wavelength. On the other hand, numerical simulations of the modulating electric field distribution, the modal field distribution, and Γ at different wavelengths were carried out; the calculated relationship between Γ and wavelength is in good agreement with the measured results. Further simulations indicate that as the wavelength increases, the center of the modal field profile gradually moves toward the weak electric field side from the waveguide surface, thus leading to a smaller Γ at a longer wavelength. Such a relationship between Γ and wavelength is partially responsible for the nonlinear dependence of Vπ on wavelength obtained experimentally. This would be useful for designing and optimization of LN waveguide-based devices.