The existence of defects significantly affects the quality of underground engineering, making it necessary to detect the existence of defects with geophysical methods. The fluctuation characteristics of Rayleigh wave in the medium containing defects were analyzed with the finite element method, and quantitative analytical methods of shape parameters and position of defects were proposed. The horizontal position of defects is defined based on the propagation time difference between the incident Rayleigh wave and the reflected Rayleigh wave, while the depth of defects is obtained with the critical disturbance frequency method.The size of defects is determined with the energy attenuation rate method. The results show that the energy of Rayleigh wave attenuates and reflects during the process of propagation along the surface of the medium. It can be observed that results from the proposed method are in good agreement with the measured data.