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.