The Integrated acousto-optic tunable filter have the potential to perform the OADM or OXC functions, which play significant role in WDM optical network. The characteristic of the acousto-optic mode conversion is sinc2-like functions with high sidelobe intrinsic. The high sidelobe level lead to serious crosstalk in the WDM optical network. The theory of weighted coupling for IAOTF has been presented. And the filter response using four suggested weighted functions has been calculated with the matrix methods. Significant suppression of sidelobe level has been achieved by employing the techniques of weighted coupling. It is a valid approach to reduce the sidelobe of IAOTF by chosing propriety weighted function and a realized way.