A　novel　optical　current　sensor　based　on　radial　grating-polarizer　(RGP)　detection　is　proposed　in　this　paper　to　realize　a　linear　measurement　of　currents　for　power　systems.　The　sensor　mainly　consists　of　a　magnetic　concentration　ring,　a　newly　designed　RGP,　an　image　converter,　and　an　image　acquisition　and　processing　system.　The　grating-polarizer　is　employed　to　convert　the　polarization　plane＇s　rotation　of　a　linearly　polarized　light　into　the　rotation　of　a　circular　facula,　which　then　be　converted　into　the　horizontal　linear　movement　of　a　linear　facula　by　an　image　converter.　Thus,　a　Faraday　rotation　angle　can　be　measured　directly　by　positioning　the　dark　stripe　in　the　facula.　A　110-kV　prototype　with　the　rated　current　300　A　is　completed,　and　trail　run　on　the　line.　The　performance　shown　that　it　meets　the　national　standard　of　0.5%　accuracy　class,　and　can　achieve　the　linear　measurement　of　the　Faraday　rotation　angle　in　the　range　of　+/-　45　degrees.