A distributed multiple-input multiple-output synthetic aperture radar (MIMO-SAR) system combines azimuth multi-channel and digital beamforming technologies to produce data with a high-resolution azimuth and wide swath. The MIMO-SAR system uses a tight along-track formation, and the spacing between its satellites is typically 100 m. The space sampling characteristic is sensitive to changes in pulse repetition frequency (PRF). This paper presents a method for optimizing the PRF of a distributed MIMO-SAR system based on the performance of the latter. The optimized PRF adapts well to variations in satellite spacing. These results show that PRF optimization can effectively improve the performance of the distributed MIMO-SAR system.