Abstract: When ideal Bessel beams propagating in free space, their intensity patterns in every plane normal to the propagation axis are unaltered and highly localized. Due to their novelty characteristics, such as small center spot diameter, high intensity, long depth of field, good direction, and long propagation distance. At millimeter and sub-millimeter wavebands, Bessel beams may be useful in imaging, measurement and realization of remote bunching propagation of electromagnetic energy in space.In this paper we use the FDTD method to analysis and study the scattering characteristics of Bessel beams when it encounter with metal or other media. In the FDTD method we lead Bessel beams into the target area at the connection boundary. The beams will be scattering when it come with metal and dielectrics cylindrical or square columns, so we use the extrapolation method to get the RCS of the target media.