Abstract: Compared with the traditional strip map mode, as a new imaging mode, Circular Scanning SAR (CSSAR) can be used to perform imaging with a wider area in a shorter time. However, due to the influence of the circular orbit, it is difficult to obtain the two-dimension spectrum of the target echo signal which brings a lot of obstacles to the following imaging processing. Thus, a new method for CSSAR imaging based on series reversion is proposed in this paper. By unfolding the Doppler frequency, the stationary phase point expansion coefficients are obtained, making it easy to access the signals two-dimension spectrum, through which range compression and range cell migration correction can be implemented effectively. Furthermore, the accuracy of the spectrum is controlled by keeping enough terms in the two series expansions, which is helpful to the imaging analysis and the following processing. Finally, the feasibility of the proposed approach is validated with the point target simulations and the comparison results.