According to the acoustic principle, when the pressure wave reaches the back interface of the stone, the reflected tension wave will be generated because the acoustic resistance of the stone to the surrounding liquid or tissue is reduced. Because the compressive strength of most stones is only110 of tensile force, that is, they can bear the extrusion force of pressure wave, but not the tensile force of tension wave. Once the tensile failure strength of stone is exceeded, this reflective tensile wave will cause spalling failure. In addition, after extracorporeal shock wave lithotripsy, crystal separation and rupture can also be seen in concentric layer stones. This failure mode is caused by the acoustic impedance mismatch between the crystal layer and the peripheral matrix layer, which leads to the reflected shock wave between the layers. According to the same mechanism, the propagating shock wave interacts with the structural defects inside the stone, which can produce a large number of tiny cracks. These cracks gradually expand and extend under the repeated action of the shock wave, forming a larger fracture line, which eventually leads to the complete crushing of the stone.