Abstract: According to the electromagnetic propagation characteristics of Ground Penetrating Radar (GPR) in the medium, how to identify the target in coal seam using the relative permittivity of the dielectric object is studied, the identification algorithm of dielectric object based on electromagnetic echo field intensity with propagation loss and reflection loss are analyzed. The simulation results show that coal seam attenuation coefficient has extremely weak influence for echo field strength, when the relative permittivity of the dielectric object is less than 3, the phase of incident wave is the same as it in echo, when the relative permittivity of the dielectric object is more than 3, the situation is just opposite. Therefore, according to the echo field strength can probe gas and water contained in coal previously and efficiently and provide pre-judgment basis for the safety of coal mine.