Abstract: The paper analyzed transmission characteristics of high-frequency electromagnetic wave of underground wireless channel,put forward that electromagnetic wave transmission has multi-path fading effect because of diffraction,reflection and scattering of obstacle such as coal seam,coal wall and underground working equipment.The paper introduced simulation and research method which used to study effect of distance of electromagnetic wave transmission on multipath fading and RMS delay,namely principle of ray tracing method,adjustment of ray direction in track process and calculation of field strength value of ray. Based on the research method,the paper also studied effect of distance between transmitter and receiver on propagation loss and RMS time delay spread of the electromagnetic wave in idealization model of incline tunnel.The simulation result showed that closer distances between transmitter and receiver,less transmission loss;lower central frequencies of electromagnetic wave,less transmission loss;longer distances between receiver and transmitter,higher RMS delay value of electromagnetic transmission.