HF band is a severe electromagnetic environment in which HF backscatter system works. All kinds of interference in this band having a strong impact on the system’s performance must be suppressed. Through analyzing the interference of the measured data of HF backscatter system

we find that some interference appears strong correlativity between adjacent range units.and between adjacent Doppler units

respectively. Aiming at this kind of interference

an interference suppressing method which is based on eigen subspace in Doppler field is proposed. The method is: firstly

interference convariance matrix is constructed in Doppler field

after eigenvalue decomposition of this matrix

the interference subspace is obtained

then the pending units are projected to the orthogonal supplement of the interference subspace

finaly

the interference is excised. The results of applying this method to the measured data show the effectivity of the proposed method.