The polarization spectral intensity modulation (PSIM) is an advanced polarization spectral measurement technology, and the measured data processing is the key link of PSIM to resolve the polorization spectrum information. The mathematics principle was presented on how all elements of Stokes vector spectrum of LUT are extracted from the measured data of PSIM system, starting from the modulation mechanism of PSIM technology, combined with relevant theory of digital signal processing (DSP), and the procedure of measured data processing for PSIM spectropolarimeter system was established. The spectropolarimeter experimental device based on PSIM was set up, and the measurement experiment was carried out, so that the light from the parallel light pipe directly and the polarized parallel light pipe output by polarizer were measured respectively. The measured data of the experimental device was processed according to the data processing procedure established previously to extract the spectropolarimetric information from it. The good consistency between the results of theoretical analysis and that of data processing verifies the method of data processing of spectropolarimeter based PSIM is correct.