Abstract: During the excavation of the roadway, using reflected in-seam waves detection technique to explore the structure of roadway and accurately interpret the wave impedance interface is of signality for mine production. The method of detecting the position of faults by reflected in-seam waves is usually inaccurate, which is mainly caused by the selected deviation of reflected in-seam waves velocity. In order to reduce the selected deviation of reflected in-seam waves velocity, this paper analyzed the features of reflected in-seam waves velocity of fifteen coal seam in thirteen coal mines and the velocity relationships of reflected in-seam waves, direct in-seam waves and transmitted in-seam waves were summarized, it was found that the velocity of the reflected in-seam waves was 3%-12% higher than that of the direct in-seam waves, and 1%-6% lower than that of the transmitted in-seam waves. The research results were introduced to the reflected in-seam seismic detection project of a coal mine in Shanxi Province, and the fault location interpreted by the in-seam seismic exploration deviated only 3 m from that exposed by roadway, which proved the application effect was well. This research provides a new idea for improving the detection accuracy of reflected in-seam waves.