Passive millimeter and terahertz wave imaging is a powerful way for personnel security inspection and scene monitoring. The existing systems usually have a single polarization mode. To obtain more information, polarimetric imaging has been preliminarily explored recently. However, there is no work exhibiting high-performance polarimetric imaging to analyze and interpret polarization characteristics. In this Letter, we report on the development of a W-band passive polarimetric imaging system for human body screening and present the polarization characteristics analysis of several typical scenarios. The experimental system has a spatial resolution of better than 2 cm at 2.5 m distance and has a thermal sensitivity of better than 0.3 K. The system can display polarization properties of human bodies and concealed objects. The experimental results demonstrate that passive polarimetric imaging has a great potential for object contrast enhancement, detection, segmentation, and recognition.