Aimed at solving the problem of typical defects of shield tunnel lining, this paper established the numerical dielectric models. Numerical simulations of radar wave performance in models for typical detects were conducted. The simulation algorithm used was the finite difference time domain solution, with the perfectly matched layer absorbing boundary conditions for these attenuation models. The scattering of the steel-bars in the tunnel segment was fully considered during FDTD simulation. The simulated results could be a good guide to GPR data collection, processing and interpretation for shield tunnel lining detection.