Abstract: Radar weak target detection under complex background has always been a worldwide difficult problem in the field of radar signal processing. With the development of novel radar system, more spatial dimensions can be provided for signal processing. Orthogonal waveform multiple-input-multiple-output (MIMO) radar's wide-transmission and narrow-reception with ubiquitous observation can effectively extend the dwell time of the target. It can realize the joint signal processing in the time, space, and frequency domain, and high-resolution estimation, thereby helping to accumulate target’s energy and suppress clutter, which can improve the ability for weak and small targets detection in strong clutter background. In view of the advantages of orthogonal waveform MIMO radar, the recent research progress of long-time integration and target detection technology are summarized in this paper. The concept and classification of orthogonal waveform MIMO radar long-time integration are introduced. Effective solutions of maneuvering targets integration using orthogonal waveform MIMO radar are provided from the aspects of characteristics of maneuvering target, transform domain coherent integration, tracking-before-detection, long-time coherent integration, and sparse time-frequency analysis etc. Finally, the problems in the existing research are summarized, and the future development of technology is provided as well.