Arch roadway is most common type of roadway in coal mine. The propagation characteristic of electromagnetic wave in an empty arch roadway was analyzed. Using the waveguide theory and the numerical calculation method,the formulas of attenuation rate in an empty circular roadway are given. The influences of transmission frequency,cross sections of roadway and dielectric parameter of surrounding rock on attenuation rate of electromagnetic wave transmission were simulated. The results showed that at 300 ～ 3000 MHz the higher the work frequency is,the smaller the attenuation rate is; the larger area of cross section is,the lower attenuation rate is; the attenuation rate increases as the relative dielectric constant of surrounding rock enlarges,and the effect of variation of the dielectric constant on vertically po-larized wave is greater than that of horizontally polarized wave; the influence of conductivity of surrounding rock on the attenuation of electromagnetic wave was minor and could be ignored.