The production of spin-polarized electrons and the modulation of polarization direction with liquid crystal variable retarder (LCVR) are discussed. The LCVR ca n play the roles of 1/4, 1/2, 3/4 and whole-wave plates with special voltages in the optical system. And the advantages of using LCVR instead of Pockels cell an d 1/4λ plate are the insensitivity to the incident photon direction, and the va riability of retardation over a large wavelength range without mechanical moveme nt. The polarization direction of spin-polarized electrons can be modulated easi ly by switching the helicity of the circularly polarized light. In order to dete rmine the photon polarization, the spinning polarimeter is developed. And the re sult is also described.