The invention discloses a detection method for the concealed fault nature of a working face based on reflected in-seam waves. The way of separately arranging multiple detectors in combination with multiple motivating drill holes in roadways on two sides is used, each drill hole in the roadway on each side is sequentially motivated at intervals to serve as multiple earthquake origins; the multipledetectors separately receive reflection in-seam waves for many times, an earthquake host acquires a position relation between two discs of an internal fault plane according to reflected in-seam wave signals received for many times and the position relation between the motivating drill holes and the detectors; and displacement in the horizontal direction and displacement in the vertical direction of the two discs of the fault plane are finally acquired after three-dimensional modeling and meshing subdivision and displayed on a three-dimensional model. According to the method provided by the invention, the detection roadway is not needed to be additionally arranged, the relative displacement between the two discs of the fault plane can be accurately measured through detecting the reflected in-seam waves, and thus the blind fault in the working face is displayed in a transparent manner.