In　order　to　obtain　the　accurate　design　parameters　of　acousto-electro-optic　(AEO)　devices,　the　geometrical　relationships　of　anomalous　acousto-optic　effect　are　studied　by　tangent　condition　and　matching　condition.　Angle　relationships　of　incident　light　vector,　diffractive　light　vector　and　optic　wave　vector　are　determined.　Curves　of　extreme　frequency　and　acousto-optical　(AO)　merit　for　different　ultrasonic　waves　in　xO3　plane　are　systematically　given.　Further　on,　the　design　parameters　under　different　central　frequency　are　also　calculated.　The　results　show　that　parameters　gained　by　this　way　are　more　precise　comparing　to　that　gained　by　solving　Dixon　equations.