To develop polarizer functioning in the extreme ultraviolet （EUV） and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility （BSRF）. The reflectivity of the synthetic mica crystal at an angle of grazing incidence of 48° was obtained from the experimental data, which is about 4.8 × 10-3 at 25 nm and 6.0 × 10-4 at 12 nm, and the linear polarizance of the X-ray reflected by the synthetic mica crystal that we measured using an analyzer-rotating method increases from 80% to 96.6% in this EUV region, while higher than 98.2% in the simulation. The result indicates that this synthetic mica crystal works as a practical polarizer in this EUV region of 12-25 nm, and also in an extensive wavelength region higher than 25 nm.
