Multi-input multi-output (MIMO) radar which has evident advantages in many applications is a new radar system.Applying the MIMO technique to the earth observing synthetic aperture radar (SAR) system offers effective ways for the improvement of high resolution and wide swath imaging and ground moving target indication (GMTI) systems.Designing the optimal orthogonal waveform is a crucial problem in the research on MIMO radar.First,the index definition of synthetic integrated side-lobe level ratio (ISLR) is proposed by focusing on the SAR application and considering the cross-correlation energy influences between orthogonal coding signals with the same frequency band.Second,it is theoretically demonstrated that the performance of synthetic ISLR of orthogonal coding signals with the same frequency band cannot meet the demands of SAR imaging,which has been proved by one-dimensional numerical simulation. Third,it has been shown through numerical simulation that the performance of synthetic ISLR of orthogonal coding signals still cannot be improved by dealing with the mismatched filtering.Finally,a set of orthogonal phase coding signals are designed for multiple MIMO-SAR antennas.The conclusions are verified through MIMO-SAR imaging and InSAR simulation experiments. Multi-input multi-output (MIMO) radar which has Replicated advantages in many applications is a new radar system. Applying the MIMO technique to the earth observing synthetic aperture radar (SAR) system offers effective ways for the improvement of high resolution and wide swath imaging and ground moving target indication (GMTI) systems. Designing the optimal orthogonal waveform is a critical problem in the research on MIMO radar. First, the index definition of synthetic integrated side-lobe level ratio (ISLR) is proposed by focusing on the SAR application and considering the cross-correlation energy influences between orthogonal coding signals with the same frequency band. Second, it is theoretically prototype that the performance of synthetic ISLR of orthogonal coding signals with the same frequency band can not meet the demands of SAR imaging, which has has proved by one-dimensional numerical simulation. Third, it has been shown through numerical simulation that the performance of synthetic I. SLR of orthogonal coding signals still can not be improved by dealing with the mismatched filtering. Finally, a set of orthogonal phase coding signals are designed for multiple MIMO-SAR antennas. The conclusions are verified through MIMO-SAR imaging and InSAR simulation experiments.