Abstract With the fast development and extensive application of Synthetic Aperture Radar(SAR), There are more and more interference and jamming to SAR. It is necessary to assure performance of SAR imaging to enhance the ability of interference suppression. This paper analyzes the characteristics of the common Narrow Band Interference (NBI). A new approach for NBI suppression is proposed, which uses eigen-subspace based filtering on the echo data of SAR. Simulation results of SAR show that the proposed approach can suppress the NBI effectively.