Multiple input multiple output synthetic aperture radar (MIMO SAR) can solve the high resolution and wide swath imaging conflicts of traditional SAR. To improve the suppression capability of MIMO SAR for echo signal interference between different channels, we adopted multidimensional waveform encoding technology to design system and studied the waveform design of MIMO SAR. Two typical signals in MIMO SAR (positive and negative linear frequency modulation signal and orthogonal frequency division modulation chirp) were selected and compared with short term shift orthogonal (STSO) signals. Considering the characteristics of multiple apertures simultaneously transmitting signal and receiving echo, MIMO SAR was combined with multidimensional waveform encoding technology for echo processing. Digital beam forming technology was used to divide multiple subswaths in distance dimension to achieve large mapping band imaging. In azimuth dimension, multichannel reconstruction algorithm was adopted to restore the periodic non-uniform sampling echo to uniform sampling, so as to achieve high resolution imaging, and then the design and imaging of the new SAR transmitting signal were carried out. Experimental results show that compared with other two signals, STSO signal had the best performance in terms of peak side lobe ratio, integral side lobe ratio, and resolution, which could suppress the fuzzy energy more thoroughly. STSO signal performed well in MIMO SAR, which was similar to that in traditional SAR. Besides, STSO had better focusing performance in MIMO SAR system with good imaging indexes, which could reduce system complexity.