The　real-time　linear　measurement　of　the　Faraday　rotation　angle　of　polarized　light　based　on　the　crystal　wedge　is　presented.　Compared　to　the　traditional　methods,　the　measurement　based　on　crystal　wedge　is　not　only　insensitive　to　the　light　power　fluctuation,　but　also　can　realize　the　real-time　detection　due　to　no　adjustment　of　the　optical　elements　during　the　experiments.　More　importantly　the　linear　measurement　can　be　kept　for　any　polarization　angle,　and　the　relative　accuracy　reaches　8.7×10-4.　The　Verdet　constants　of　the　Bi:YIG　magneto-optical　film　with　Tb　doping　under　various　temperature　are　investigated　by　this　method,　and　the　temperature　dependence　is　analyzed.