Abstract: In the frequency-stepped chirp signal, the frequency spectrum overlap between the neighboring sub pulses would lead to grating lobes in the result of range compression. The weaker points may be masked or distorted by the grating lobes of strong points. In this paper, a grating lobe suppression algorithm is proposed based on apodization filtering. By weighting the spectrum of sub pulse signals with different functions, the apodization could be done through the results and the grating lobes could be eliminated. Numerical simulations and real data experiment confirm the effectiveness of the proposed algorithm.