A novel coherent deception jamming method based on time-modulated technology for Synthetic Aperture Radar(SAR) using linear frequency modulation (LFM) signal is proposed in this paper. By periodically modulating received SAR signals with radio frequency switches, the jamming signal summed by harmonics which are equivalent to corresponding frequency-shift of incident LFM signals, is generated. Supposing that the jamming echo is processed by the range compression, the range migration correction and the azimuth compression, the closed-form expression of the SAR imaging output is derived and false targets can be obtained. Numerical simulation results are provided to verify the effectiveness of the proposed method.