Abstract -- The purpose of this study is to investigate the underground sound generated by different kinds of rock motion occurred in the debris flows, mainly the friction and collision between two rocks. Effects of the stone material on the characteristics of underground sound are studied systematically. The sound signals are analyzed using both the fast Fourier transform and the Gabor transform to represent the signals in the frequency and time-frequency domain. The experimental results reveal that there is no apparent difference in the frequency of sounds generated by the friction and collision between two stones, although the sounds may differ in pressure. The frequency of the underground sound generated by the friction and collision between two stones can be divided into three regions, namely 10-100 Hz, 120-300Hz, and 400-800Hz. A statistical method and the trapezoidal characteristic curve of fuzzy theory are applied to identify the similarity of the underground sound generated by different rock materials.