Coal is important energy resource for China with complex mining conditions. With the increasing of mining depth and intensity, the demand for fine detection of coalfield micro- structure is increasing. In- seam wave exploration technology is an effective means to obtain the fine geological structure information of coal seam working face because of its advantages of high detection accuracy, strong anti- interference ability and easy identification of waveform characteristics. However, the seismic wavefield in underground coal seam is complex, and the wavefield characteristics of reflected in- seam wave need further study. In this paper, we study the 3D in- seam wave numerical simulation technology in underground coal mines. Different types of 3D coal seam geological models with faults are designed, and the reflected in- seam waves are simulated by 3D staggered grid high- order finite difference algorithm. The wavefield characteristics of reflected in- seam waves are analyzed, and the influences of faults with different dip angles and different fault distances on reflected in- seam waves are discussed. The effective reflected in- seam wave is obtained by removing the interference wave technology, and then the reflected in- seam wave is processed by envelope superposition. The dispersion of in- seam wave is suppressed effectively, the event converges obviously, and the energy is more concentrated, which provides a good data basis for the subsequent imaging processing.