Abstract: Synthetic bandwidth technology realizes super range resolution by fusing multi-band stepped chirp signal. The mode that transmitting and receiving sub-band signal in consequence with single phase center imposes strict request on pulse repetition frequency (PRF), which means that this mode is not suit for high resolution wide swath imaging of space-born SAR. This thesis focuses on multiple-input multiple-output (MIMO) SAR based concurrent-sub-band system, interprets the principal of signal processing, pointes out the indispensability of correction of azimuth positions. Because of the overlap between neighboring sub-band, unwanted virtual image is unavoidable . The mechanism of the virtual image is interpreted in detail, stepped frequency up and down chirp signal based approach is put forward to suppress the peak level of the unwanted profile, the validity of the approach is demonstrated by simulation results.