In this paper, the modulation characteristics of a reflective type standing wave acousto optic modulator are analysed theoretically. In order to ensure forming of a strong standing wave ultrosonic field in the acousto optic interaction substance and the higher modulation efficiency of devices by increasing the length of the acousto optic interaction substance and improving the matching network and so on, some methods regarding the design and manufacture of the modulator are proposed. Thereby, a modulation efficiency of 50% for the zero order light of a He-Ne laser under the injecting power of 1 W is obtained.