S-band High Power Microwave(HPM) is employed to produce the plasma in the atmosphere environment simulation chamber. The experiment researches on Ka-band microwave propagating characteristics in atmospheric plasma are performed, and the Ka-band microwave attenuation characteristics of atmospheric plasma are obtained. Some novelty propagation characteristics in the interaction of electromagnetic wave and atmospheric plasma are found: the electromagnetic wave transmission signal enhancement effect appears oscillation on Ka-band; the maximum value of propagation enhancement is almost 2 times, and the period of oscillation is 80 MHz. The phenomenon of propagation enhancement also occurs with the enhancing of buffer gas pressure, but the amplitude decreases. The reasons of propagation enhancement are analyzed. The research results provide important technical support for the application of plasma in stealth and black barrier communications.