The article introduces a kind of broadband acousto optic deflector based on gallium phosphide crystal. The device adopts the structure of quasi ultrasound track design, which greatly improved the total work length of the transducer, and implements the reasonable consideration of the bandwidth and diffraction efficiency. The device is provided with 3 dB bandwidth of 900MHz, the diffraction efficiency 8%@1 W, and the dynamic scanning angle outside the acousto optic medium of 5.2°. Meanwhile, an abnormal phenomenon is found during the experiment, a redundant diffraction light spot appears between the first degree and secondary diffraction light spot (which is named “fake spot”). The mechanism of the fake spot needs to be further studied.