At present, the main problem faced by the millimeter wave (MMW) radar imaging system is how to use the minimum antenna array to achieve high resolution. The introduction of multiple input multiple output (MIMO) array technology into the radar imaging system can reduce the number of array elements, and the combination of synthetic aperture radar (SAR) technology can effectively improve the resolution. However, in the actual imaging system, due to the mismatch of the amplitude and phase of the antenna array on the radar board, the imaging results will appear artifacts and range offset. Therefore, on the basis of the MMW imaging algorithm, the paper focuses on the calibration algorithm, proposes a two-dimensional plane calibration algorithm based on the corner reflector, realizes the accurate estimation of the coordinates of the corner reflector through the phase change and the least square method, realizes the simultaneous calibration of the distance and phase of each channel of the MIMO array. Besides, we build the MIMO-SAR MMW imaging system and carry out the MIMO-SAR imaging and calibration experiments. Finally, the feasibility of the imaging and calibration algorithm is verified by the experimental results.