In the paper, the polarized light signal is analyzed in theory and a corresponding mathematical model is established. The collected data are dealt with the least-squares-fitting, and so the polarization vector is obtained. The high precision may be obtained, and the digit of A/D converter and the accuracy of the modulating frequency are key factors. The measuring system with a simplified mechanical and electrical structure is presented in the paper. The system is adapted for the rapid and long-distance measuring.