Millimeter wave characteristics differ from those of microwaves, infrared or optical system, and it has some distinct advantages over microwave, infrared, or optical system. Currently, passive detection techniques with the Millimeter Wave (MMW) radiometer play important role in homing guidance of anti-armour missile and end-sensing-cartridge. In view of the factors such as kinetic energy of the target, the target’s temperatures are changing. This paper studied on the radiometric characteristics of the changing temperatures target with passive millimeter wave seeker. The relationship among the electrolytic coefficients, radiometric characteristics of the changing temperatures target and the radiation of the targets was analyzed based on the experiments. Moreover, the angles of detector and the detection distance were analyzed. And then, the main factors for the method of passive MMW stealth technology were given.