ing at the influence of the polarization aberration caused by the freeform surface on the imaging quality and measurement accuracy of the system, the polarization aberration analysis method of the freeform off-axis optical system with fringe Zernike polynomial is proposed based on Jones representation, and an analytical model of polarization aberration for freeform reflection optical system is constructed, and the effects of Z₅ and Z₆ in fringe Zernike polynomials on the polarization aberration distribution of off-axis field of view optical systems are analyzed. Through the tracing of the polarized light in the full field of view, it is verified that the freeform surface acts on the three polarization aberrations of the field of view off-axis optical system, such as phase aberration, diattenuation, and retardance. A full-field polarization aberration analysis is carried out for a large field of view off-axis three-mirror optical system with freeform surfaces. The analysis results show that the phase aberration distribution is consistent with the vector height distribution of the freeform surface, and the two-direction attenuation and phase delay are 50% of the total system.