Unlike the traditional direct current millimeter-wave radiometric imaging, an alternating current radiometer was first presented for the passive millimeter-wave imaging with simple and integrated structure in China. On basis of discussing the special structure and energy spectrum, the energy compensation mechanism and image description of an alternating current radiometric imaging were also analyzed. Lots of indoor and outdoor experiments were carried out for the different application such as safety inspection. The imaging results of 3mm band alternating current radiometer show that the alternating current radiometric image possesses its own characteristic different from the direct current radiometer. The alternating current radiometer is easy to realize passive millimeter-wave multi-channels focal plane imaging.