Ground-penetrating radar (GPR) is one most effectively technology of researching some unify scientific problem, such as hydrology, environment, climate change, disaster and archaeology etc. It can detect engineering construction, road, building internal structure, permafrost layer and internal structure of desert. It has some advantages, including rapid detection, higher resolution and directly-vision imaging. However, Due to have influence on the change of lateral radar velocity, the diffraction of isolated block, it ' s difficult to effectively reflect the inner fine structure at subsurface from GPR section. The process of migration can improve the resolution. Combined with traditional Kirchhoff migration, reverse time migration (RTM) can effectively use reverse branch wave and multiple-wave to image subsurface,make the underground reflection point information back to properly position reflections,and the reflection wave simultaneously, the diffraction wave automatic convergence,which can adapt to medium of lateral velocity changes and high resolution for imaging to dip interface. In this paper, we deduced the finite-difference scheme of TM wave equation from Maxwell' s equations, stability and PML boundary condition. The result of RTM imaging of two layers model and cavitas model are same with the original their velocity model,respectively,which can demonstrate the accurate of the finite-difference zero-offset RTM algorithm. Combined with Kirchhoff migration section of two layers model and cavitas model, RTM sections can more effectively improve the resolution of the vertical interface and bottom boundary of cavitas,and can more really reflect the space position and inner structure of two layers model and cavitas model.