For the detection of concealed objects, radar technology is commonly used at present and ground penetrating radar, wall penetrating radar and other technologies have also been developed.Millimeter wave can be used for imaging and has certain penetration capability.The millimeter wave radiometer can work all-weather day and night.What‘s more, the detection system is relatively small in size, low in cost and convenient to use, which makes it more and more attractive.In this paper, a radiometric imaging system is used for shallow-buried metal object detection, the region growing method is used for extracting the interested single target, and the center of the target is calculated based on its radiation temperature.Experimental result shows that, the method can detect the shallow-buried metal targets and extract the interested single target and its characteristics, which can be used for further application.