Abstract: According to the classical dispersion theory, we derive the dispersion law of medium to high frequency electromagnetic wave. From this law we know that almost all the mediums are transparent for high frequency electromagnetic wave. Therefore, the latter can pass through the former. This conclusion is proved with copper for an example. One can understand some application about high frequency electromagnetic wave by means of this conclusion.

Key words: electron, medium, high frequency electromagnetic wave, index of refraction, dispersion