Abstract: Using analytical method and numerical method, the paper emphatically researches propagation characteristics of electromagnetic waves in circular tunnel, rectangular tunnel and arched tunnel. A conclusion is made that the larger area of cross sections is, the lower attenuation rate is, and shape of cross sections affects on attenuation rate too. When frequency is comparatively high, circular tunnel, rectangular tunnel and arched tunnel have same formulation of attenuation rate. When the radius or half of larger side is ten times larger than the free-space wavelength, attenuation rate is very low and hardly related to the shape of cross sections, and only related slightly to the area of cross section of tunnel.