Aiming at the problem that the diffraction phenomenon generated in the long-wave infrared (LWIR) polarized optics system containing digital micro-mirror device (DMD) will lead to the change of the polarization aberration in the system, which will cause a decrease in the accuracy of the polarization measurement of the LWIR polarized optics system, we propose a method for analyzing and compensating for the polarization aberration of the LWIR secondary imaging optical system containing DMD. Firstly, Based on the ratio of wavelength to DMD pixel size in the LWIR polarized optics system, a diffraction and polarization aberration characteristic transmission model is constructed and a polarization aberration analysis method based on the Jones vector theory of vector diffraction-polarized light is proposed. Secondly, the polarization aberration and polarizability of DMD are deduced to determine the optimal diffraction order, incidence angle and diffraction efficiency of DMD, and then the secondary imaging LWIR polarized optics system containing DMD is designed to obtain the influence of DMD diffraction characteristics on polarization aberration. Finally, the polarization aberration of the optical system is compensated by tilting the projection objective, coating the lens and reducing the surface incidence angle, so as to solve the influence of diffraction phenomenon on the polarization aberration of the LWIR polarized optical system. Simulation results show that the full-field-of-view modulation transfer function of the system is close to the diffraction limit at the cut-off frequency, the maximum aberration is less than 0.2%, the imaging quality is good, and the two-way attenuation of the whole system is reduced to 1/12 of the original one after compensation. This analytical model can reveal the relationship between diffraction and polarization aberration, and the compensation method can effectively reduce the polarization aberration.