Passive millimeter wave imaging is an important development direction in the field of public security. Nowadays, the researchers at home and abroad mainly concentrate their efforts in the reflex systems with focal plane arrays. This will result in a high development cost. Moreover, the fabrication of large diameter off-axis paraboloidal mirrors is more difficult. By combining geometrical optics with Gaussian beams, a quasi-optical system suitable for near field passive millimeter wave imaging is designed and developed on the basis of a millimeter wave lens. The system has a detection range of 1.5 m, an imaging area of 1.2 m×1.2 m and a spatial resolution better than 3 cm. Because the system can implement non-contact security inspection, it has a wide application prospect in various public inspection places.