A　new　method　of　measuring　the　Faraday　rotation　angle　directly　in　optical　current　transducer　(OCT)　is　proposed　based　on　conoscopic　interference　pattern.　The　concept　of　conoscopic　interference　and　isogyres　is　illustrated.　The　relationship　between　the　isogyres　angle　Φ　and　the　polarized　plane　rotation　angleθ　caused　by　the　polarizer　rotation　is　deduced　toθ　=　2Φ　.　This　rule　can　be　used　to　measure　the　Faraday　rotation　angle　in　OCT　according　to　the　Faraday　magneto-optic　effect　when　a　linear　polarized　light　beam　passing　through　a　crystal　and　current　magnetic　field　acting　on　it　at　the　same　time,　the　polarized　plane　will　be　rotated　and　the　angle　of　isogyre　will　be　changed.　An　experiment　is　designed　to　demonstrate　the　relationship　between　the　coil　current　and　the　isogyre　angle.　CCD　camera　are　used　to　capture　the　conoscopic　interference　pattern　to　measure　the　current　of　coils,　the　angle　of　isogyre　is　calculated　by　image　processing　technology.　The　measuring　range　is　18　times　of　traditional　OCT.　This　experiment　proves　the　relationship　between　the　isogyres　angle　Φ　and　the　polarized　plane　rotation　angleθ　,　and　the　linear　relationship　between　the　current　and　the　isogyre　angle　is　realized.　©　2011　Published　by　Elsevier　Ltd.