In the paper, a weighted-coupling scheme of a SiO2 film-loaded Ti:LiNbO3 quasi-collinear integrated acousto-optic mode converter is reported, in which an angular offset between the acoustic and optical waveguides is introduced to implement an optimized Hamming weighted function for realization of ultralow sidelobe level. Acoustic wave guiding properties have been investigated for films such as SiO2, ZnO on LiNbO3 firstly. SiO2 film on LiNbO3 was selected as acoustic waveguide. With the mode analysis of the acoustic wave guide and the theory of coupling mode the limit of the width, weighted coupling coefficient and the characteristics of the conversion of acousto-optic modes are obtained. As the angle between acoustical and optical waveguides guides is 0.45ο, the worst sidelobe level is −16.8dB and the theoretical values of bandwidths of−3dB and −10dB is 1.37nm and 2.31nm respectively, which have excelled the domestic reported level.