When a metallic target is coated with plasma, the plasma will absorb and refract the incident electromagnetic wave, so as to attenuate the power of the incident wave and reduce the power of the reflected wave. Thus, the RCS of the target also will be reduced. For the uniform magnetized plasma, the permittivity has a relationship with the density of particle of plasma, the intensity of the outer magnetic field, the collision rate of electron and the frequency of the incident wave. The influence of different density, intensity, collision rate and thickness on the attenuation and reflection characteristics of electromagnetic wave in millimeter wave band can be calculated by the simulation method.