Based　on　the　encoding　requirements　of　the　continuous　variable　coherent　optical　communication　in　the　single　beam　light,　a　novel　encoding　scheme　by　the　joint　modulation　including　magneto-optic　modulation　and　electro-optic　modulation　was　proposed.　According　to　the　mapping　relationship　between　Stokes　parameters　and　Poincare　sphere,　the　coding　principle　of　the　joint　modulation　is　analyzed　in　Stokes　matrix　theory.　Then　a　single　beam　optical　system　is　set　up　for　encoding.　And　based　on　the　needs　of　encoding,　a　driving　circuit　of　magneto-optic　modulatior　and　a　circuit　of　random　number　generator　are　designed.　By　homodyne　detection　technique,　the　Stokes　parameters　are　measured,　and　the　error　rate　is　estimated　by　LabVIEW　procedure.　The　raw　data　show　that　the　error　rate　is　lower　than　3.60%,　which　verify　the　feasibility　of　the　encoding　scheme.