Abstract: Cognitive radar is a new type of radar system which combines radar parameters and environmental factors. It perceives the surrounding environment based on interactive autonomous learning, and improves the overall performance of radar system by adjusting signal transmission, reception and signal processing methods. After nearly 20 years of research, cognitive radar and its key technologies have been developed rapidly. This paper comprehensively studies a large number of cognitive radar literature, gives a relatively comprehensive comparison and analysis of the structure and composition of cognitive radar, and makes a detailed analysis of its research status from the aspects of hardware technology, waveform optimization, detection, recognition, tracking, anti-jamming, networking and other key technologies. Finally, the development direction of cognitive radar is prospected.