A practical security system for human body inspection was designed and manufactured. In this system, the newest quasi-optical technology and the active millimeter wave (MMW) scanning technology were used. The experimental result showed that the system had a resolution better than 10.2 mm in an operation mode at a frequency of 35 GHz (8.57 mm). It could inspect trace powder such as 0.5 g metal or nonmetal fixture and could complete the inspection over an area of 600 mm?1800 mm within 100 s, which had met the requirement for practical use. The inspection experiment showed that the system could be used in some special applications such as noble metal detection.