Traditional polarization imaging techniques have a series of problems, such as the poor performance of real-time polarization imaging, the difficulty to realize the multi-spectral polarization imaging, and the impossibility to realize the hyper-spectral polarization imaging. In order to overcome these problems, a new theory of polarization imaging is proposed based on the signal modulation-demodulation theory. According to the proposed theory, a hyper-spectral polarization imager based on grating dispersion is proposed. The spectrum signal after polarization modulation is obtained by the polarization imager, and the hyper-spectral image and the polarization image are obtained by means of frequency-domain filtering and inversion calculation. Hence, the polarization imager can achieve hyper-spectral total polarization imaging. The polarization imaging and the hyper-spectral imaging are well combined faultlessly. The theoretical validity of the proposed polarization imager is testified through the simulation experiment.