The design goals of a spectropolarimetric system are higher spectropolarimetric resolution， a smaller and lighter system， and static measurement of the full Stokes spectrum. Therefore， the spatially modulated heterodyne interference spectropolarimetric system， which combines the technologies of intensity modulation and spatial heterodyne was proposed. While the process of all mathematical derivation was displayed， the principle and structure of the system were presented and a theoretical analysis of the interferogram data acquisition and full Stokes parameters demodulation restoration was carried out. The matching modulator module was designed and a complete design example was finished based on the parameters of the spatial heterodyne spectrometer used. A principle experimental device of spatially modulated heterodyne interference spectropolarimetric system was established in the laboratory， and the feasibility of the principle and measurement data processing flow of the system was verified by analyzing the measurement experiments and experimental data of linearly polarized light with a known polarization state. The measurement and analysis results of the experimental data are consistent with the theoretical results， and the error is less than 3% This verifies the feasibility of principle of the spatial modulation heterodyne interference spectropolarimetric system.