Abstract: The reflected in-seam waves can detect the small structure in the coal seam. At present, the researches on the reflected in-seam waves exploration are less at home and abroad, and the signal-to-noise ratio is low. In order to improve the image quality, the diffraction migration imaging method of reflected in-seam waves was investigated. The preprocessing technologies suitable for reflected in-seam waves were analyzed. Based on three-dimensional numerical simulations and actual data processing, the feasibilities of reflected in-seam waves were demonstrated for both theoretical models and practical applications. The results showed that reflected in-seam waves should do the Hilbert transform when diffraction migration imaging was used. The in-seam wave velocity is approximately constant and the diffraction migration requires only one velocity, constituting the unique advantages of reflected in-seam waves.