With its intrinsic characteristics, circular synthetic aperture radar has lately become a particular interest to the radar community. The differences of imaging processing between the circular synthetic aperture radar and linear trajectory synthetic aperture radar were compared and analyzed. The detailed comparisons containing the size of the observed area, the properties of the point spread function, and the properties of echo spectrum were carried out. It was learnt that the difficulty of the imaging processing of single-pass circular synthetic aperture radar lies on its space dependence. To overcome this difficulty, the plane circular synthetic aperture radar and multi-base line circular synthetic aperture radar imaging models were analyzed. Simulation test was carried out and the corresponding results prove the proposed analysis is valid.