Multiple input multiple output(MIMO) radar is a new kind of system radar which introduces the multiple-input multiple-output technique from wireless communication field into the field of modern radars with the combination of digital array signal processing. Due to the waveform diversity, MIMO radar has many advantages compared with traditional phased array radar. To fully understand the MIMO radar, we make a comprehensive review for MIMO radar. Firstly, the concept and principles of MIMO radar are introduced, while the relation between the MIMO radar and phased array radar is revealed simultaneously. Then, based on the performance analysis of MIMO radar, we give advantages and disadvantages of MIMO radar in applications compared with conventional phased array radar. Finally, combined with the coherent characters and advantages of MIMO radar, several potential applications are introduced.