During reentry of hypersonic spacecraft into the atmosphere, a break in the radio communication due to the presence of a plasma sheath on the spacecraft can occur. The break is commonly known as reentry communication blackout. Normally, for high density plasma, it is difficult for the electromagnetic waves of L and S bands to penetrate through. They may be decayed rapidly or reflected. That is why reentry communication blackout happens. In recent years, initiative methods are used to reduce the effects of reentry communication blackout such as by designing ideal shape for reentry vehicle, sprinkling special substances on the surface of the vehicle to improve efficiency of electromagnetic wave, adding magnetic field within the blackout area, etc. However, these methods not only fail to fully resolve the problems caused by blackout but also bring some new ones. Therefore, to resolve the problems, transmission mechanism of electromagnetic waves in plasmons should be analyzed. In this paper, we use the finite difference time domain, consider the mechanism of electromagnetic waves in a structure consisting of high-density plasma rods, and refer to the two-dimensional (2D) photonic crystal and surface wave local coupling theory. A new type of high-density plasma micro-rod cavity structure is designed. The special structure, consisting of metal cavity, high-density plasma rod, and dielectric medium filled within the cavity, is quite different from traditional 2D sub-wavelength plasma rod arrays. This kind of design takes advantage of cavity structure to couple electromagnetic wave within the plasma rod so that the surface wave diffraction transmission mode can be changed into a local coupling enhancement penetrating mode. In this paper, we investigate the plasma micro-rod cavity structures with two shapes:cylinder and square, respectively. It is found that electromagnetic waves of L and S bands can have unusual transmission properties in certain frequency ranges, such that electromagnetic waves can pass through the interior of the high-density plasma rod.