The invention discloses a stope face small collapse column detection method based on diffracted waves. The stope face small collapse column detection method comprises the steps of: setting a shot point in the middle part of one side of a belt roadway, exciting seismic waves, arranging ten wave detection points (1#, 2#, ..., 10#) in a corresponding track roadway, and acquiring seismic record through a seismograph; acquiring direct waves of the wave detection points (1#, 2#, ..., 10#) and the diffracted waves of a small collapse column from the seismic record according to a sequence of propagation time of seismic waves; searching time ti corresponding to a maximum amplitude value in a diffracted wave train received at the wave detection points (1#, 2#, ..., 10#) respectively; determining transverse and longitudinal positions of the small collapse column; and finally determining an actual position of the center of the small collapse column according to the determined transverse and longitudinal positions. The stope face small collapse column detection method can be used for positioning the small collapse column accurately, is low in cost and easy to operate, fills the blank of a method for detecting the small collapse column by adopting a geophysical method in an underground coal mine, and can play an active role in guiding safe stope operation of a working surface.