In order to study the propagation property of sonic wave for the quality detection of rock bolts using sonic reflection method, 3D FEM simulation of the dynamic responses are conducted for the anchorage system with or without defects. The acceleration response signal at bolt head is normal and attenuated quickly for anchorage system without defect both in grouting mortar and in good quality surrounding rock, and it is abnormal and distorted on interface of different mediums for the anchorage system having local defect or uncompacted mortar.