Integrated acousto optical tunable filters (AOTF) have potential application in WDM optical networks because of some advanced properties, especially, the unique property of simultaneous multiwavelength filtering. The exact coupling equations with two acoustic waves travelling simultaneously were derived. Based on the coupling equations, some numerical results of conversion characteristics are given and the fluctuation of the main peak, the center wavelength and the FWHM (full width of half maximum) are analyzed with respect to time. The reasons for serious distortion and the higher crosstalk for narrower channel sapcings are discussed. Considering the drawbacks of the collinear integrated acousto optical tunable filter in multiwavelength operation, use of quasi collinear acousto optical mode converter for improving the conversion characteristics of AOTF is proposed.