Abstract: In recent years,there were some defects in the grouting behind the lining of shield tunnels which might cause some heavy aftermaths.When some were filled in the gap behind shield tunnel segments,the propagation rules of electromagnetic waves were summed up through a lot of simulation examinations of detecting of grouting materials behind shield tunnel segments with GPR(Ground Penetrating Radar).Combining simulation examination results with the two-dimensional model based on the finite difference time domain method(FDTD),the distribution of the grouting materials could be identified accurately.It was shown that the profile of GPR might be affected evidently by three factors: the curing period,different mixture ratios and distribution of gaps and grouting materials.Meanwhile,this simulation examination was important for GPR to interpret grouting effect behind shield tunnel segments.