Abstract: Scattering of radio waves by hypervelocity object is significantly changed by the formation of ionized shock layer when it reentries the atmosphere or is flying in the near space. To study this question, the radar scattering of hypervelocity object and its flow field is simulated by parallel finite difference time-domain(FDTD) method. The simulating results are compared with the experimental results which are measured by the radars of aero physics range in China Aerodynamics Research & Development Center. Then the method is used to simulate the effect of plasma flow on the radar cross section（RCS） of a hypervelocity blunt cone under given flow situation. The results show that the simulating results are consistent with experimental results. The radar cross section(RCS) of blunt cone is affected by frequency, incident angle, radar polarization, and so on. In some special radar incident angles, the RCS of blunt cone is decreased by the flow field.