Working all day and all weather, a passive millimeter wave radiometer (PMMW) can be widely used in civil and military affairs. It can get some specific information about the material characteristics different from radar and infrared detectors. On basis of the radiometric operating range equation, the radiation cross section and stealth effect of metal objects are presented for the PMMW near-sensing application. The measurement experiments of metal solid models adopts 3 mm band Dicke radiometer with the outdoor calibration system. The sky temperature and other different surface metal objects are also measured as the contrastive experiments. The results show the radiometric temperature contrasts of solid models have remarkable difference in the bare and coated conditions, and the radiometric operating range can decrease to 60.8 %. In addition, the PMMW stealth methods through different surface treatment respectively reduce the radiometric antenna temperature contrast in some degree.