The acousto-optic diffraction experimental results of guided optical waves and acoustic surface waves in the Ti-diffusod LiNbQ3 waveguides are reported in this paper. Phe intensity of two TE modes (TE0, TEX) varying with the acoustic power is measured. For the zero-order beam, modulation approximate to 100% is obtained at 68 mW acoustic power. After simple deduction, acoustic surface displacement is obtained.