Abstract: Based on the polarized light theory，the polarization change of a linearly polarized light after 　　reflected from one or more optical elements is investigated theoretically. It is found that through appropriately setting 　　the amplitude reflection coefficients ( rs 　　，rp 　　) of optical elements，the polarization deterioration of the polarized light 　　induced by several optical elements can be lower than that induced by one element. A method for determining the 　　incidence plane of a light ray is given. In the experimental setup，the polarization maintaining ratios of two 780 nm high-reflection mirrors ( with dielectric and metallic coatings，respectively) at 45o( for both polarization angle and incidence angle) are determined to be 1 000 ∶ 1 and 40 000 ∶ 1，respectively. The amplitude coefficient ratio rp /rs and phase difference δ are in good agreement with those measured by the ellipsometry. This method and setup can， on the one hand，provide theoretical and experimental guidance for polarization-related physics experiments，and on the other hand，can be applied in scientific research and engineering fields for in-situ measurement of the reflection parameters ( rp /rs and δ) and polarization maintaining ratio of optical elements.

Key words: polarization maintaining ratio, optical mirrors, measurement setup, high detection sensitivity