A novel broadband acoustooptical (AO) surface acoustic wave interdigital transducer (SAW-IDT) scheme is presented, by using double-tapezia-electrode IDT to compensate high-frequency component of the slanted single-trapezia-electrode IDT. It makes flatter amplitude response and wider bandwidth than those of the single-trapezia-electrode IDT. At the same time, the external compensating network is eliminated. The optimal compensating factor ρ=0.12 and other optimal parameters are found by computer simulation. In the device, Ti-Diffused YX-lithium niobate substrate was applied as optical waveguide, a SiO2/In2O3 film of thickness ~150 nm as ASW waveguide and an acoustical aperture of width 110 μm, in conjunction with N=9 finger pairs. This laboratory prototype shows Bragg acoustooptical bandwidth is 55.3 MHz at 187.7 MHz, its passband slope is 0 and hollow depth is less than 1.0 dB. The RF drive power is measured to be 45 mW at mode-conversion efficiency of 99%. The device is expected to be a integrated optics acoustooptical spectroscopein spectrometer for 1.15~1.65 μm.