A　universal　simulation　method　for　3-dimensional　electro-optic　device　is　proposed.　This　method　combines　the　electro-optic　wave　coupling　theory　with　finite-element　method　for　electric　field　analysis.　By　solving　Jones-matrix　of　electro-optic　device,　electro-optic　modulation　for　arbitrary　light　propagating　direction　and　arbitrary　electric　field　direction　can　be　computed.　This　method　is　elaborated　by　taking　the　transverse-modulated　Bi4Ge3O12　(BGO)　optical　voltage　sensor　(OVS)　for　instance.　The　effect　of　inhomogeneous　electric　field　and　light　beam　shift　on　measurement　accuracy　is　discussed.　The　maximum　permitted　beam　shift　for　different　accuracy　grade　is　given.　The　method　provides　references　for　designing　and　evaluating　optical　voltage　sensor　and　other　electro-optic　devices.　©　2015,　Chinese　Laser　Prees.　All　right　reserved.