The mixed solution of reduced biquaternion generalized Sylvester equation is studied by using semi-tensor product of matrices, complex matrix representation of reduced biquaternion matrix and H-representation of special matrix. The independent elements of special matrix are extracted by H-representation method to remove the redundancy. Combined with the semi-tensor product of matrices and complex representation of reduced biquaternion matrix, the reduced biquaternion Sylvester equation is transformed into a complex matrix equation with independent variables. The necessary and sufficient conditions for the existence of the mixed solution and the expression of general solution of generalized Sylvester equation are given by classical matrix theory. A numerical example is given to verify the effectiveness of the method.