Because active millimeter-wave can penetrate through cloth and plastic materials, three-dimensional holographic images of hidden dangerous goods such as metals, drugs, explosive and knives can be acquired. Compared with a X-ray inspection system, the active millimeter-wave has almost no radiation and does not do harm to biological tissue. At present, more and more metal detectors and X-ray imagers have been replaced by millimeter-wave imaging equipment in Europe and U.S.. With the rising of China's national influence, the active millimeter-wave imaging technology will have a broad application prospect in the field of public safety.