Abstract: Depolarization of imperfect metal orthogonal twin mirrors is studied by building a geometric model of the mirrors to change the direction of light ray. The simulation study shows that linear polarization sensitivity of silvered orthogonal twin mirrors is better than that of aluminum or aurum mirrors at the range of 0.4μm～10μm, and the silvered orthogonal twin mirrors have less influence on polarization ratio than those of aluminum and aurum mirrors. Therefore, the silvered orthogonal twin mirrors are recommended to be used in remote sensing of polarization. The influence of the silvered orthogonal twin mirrors on radiance and polarization ratio is very small if the angular error is controlled within 0.5°. The depolarization performance of the mirrors is well enough to satisfy the requirement of scanning polarimeters.