The marine environment is complex and changeable. To meet the urgent needs of accurate detection and identification of oil spills, a visible/infrared dual-band common-aperture polarization imaging optical system based on a defocused plane polarization detector is designed. The optical system is evaluated by ZEMAX simulation software, and we carried out the polarization imaging oil species discrimination experiment based on the split focal plane polarization detector, which proved that for some oil species that cannot be distinguished by intensity information, the polarization information can be distinguished. It verifies the feasibility of polarization detection in the discrimination of marine oil spills, which is of great practical significance in the field of marine oil spill detection.