Abstract: Circular synthetic aperture sonar (CSAS) has broad application prospects in the fields of underwater threat target verification and battlefield environmental reconnaissance due to its plane resolution of sub-wavelength magnitude, three-dimensional imaging capability and full aspect observation capability. Firstly, the imaging principle and resolution characteristics of CSAS are analyzed in this paper. Then, the research progress of CSAS experiments at home and abroad is reviewed, and the existing problems in CSAS imaging are summarized through the detailed analysis of the key technologies such as imaging algorithms, motion compensation, three-dimensional imaging and posterior processing,. Finally, the future development of CSAS is prospected.