This paper introduces a new polarization detecting method which uses a birefringent crystal to encode the two-dimensional Stokes quantities S0~S3 into an image，so that it obtains the information of four Stokes quantities with a single detection. The paper presents the working principle and mathematical model of the polarimeter. Also, the reconstructing method，as well as the effect of system parameters is theoretically demonstrated. The encoded image is obtained from numerical simulation according to real system configuration. By using a simple algorithm, we get acceptable reconstructed images which verifies the feasibility and provides references for the design.