In recent years, a new SAR concept based on Multi-Input Multi-Output (MIMO) configuration has drawn much attention. Firstly, a review was made about the development in the field under discussion. Then, the generalized ambiguity function of the conventional SAR into MIMO SAR case was extended. Next, a detailed analysis shows that the resolution of MIMO SAR not only depends on the parameters of the waveform and synthetic aperture length, but also depends on the array geometry of the multiple transmitters and multiple receivers. Simulations with a variety of parameter combinations demonstrate the derivation and analysis.