A computational approach of scattering by buried objects is presented by using finite-difference time-domain (FDTD) method, the uniaxial perfectly matched layer (UPML), and reciprocity theorem. The numerical performance of this approach is investigated by numerical experiments. The radar cross sections (RCS) of various buried objects with different electrical sizes, shapes, dielectric constants, are computed and analyzed. The results show that for the conducting cube, the RCS curves are fluctuant, but for the sphere shape one, the curves are smooth. Comparing with scattering in the free space, the ground greatly affects the RCS by dielectric targets, but little does by conducting targets. For the buried dielectric objects, iterative steps can be evaluated by four to five round-trip traversals of the Huygens box, but for the conducting ones, the time steps can be reduced to three round-trip traversals. When the ground is lossy, the run-time can be reduced more to two round-trip traversals.