A study of step frequency radar was concerned in this paper. A new frequency-domain extracted IFFT approach (FDE-IFF％) to obtain high range resolution profile was proposed,and the mathematical principle of this new method was detailed analyzed. The simulation results were given in the end and all the results proved that the FDE-IFFT method has better capability of anti-jamming. It is more effective than conventional IFFT method and it can be widely used in step frequency radar.