Airborne circular stripmap synthetic aperture radar (CSSAR) has the advantages of short revisit time and large coverage, and thus is an attractive tool for wide-area surveillance and ground moving-target indication (GMTI). To enhance the CSSAR/GMTI system's surveillance capability and moving-target detection performance, an efficient imaging algorithm is proposed. The proposed algorithm can finely focus the stationary scene and coarsely focus multiple moving targets simultaneously without a priori knowledge of the targets' motion parameters and position parameters. Moreover, the proposed algorithm is interpolation free and can be efficiently implemented using only complex multiplications and fast Fourier transforms. Simulation results validate the proposed algorithm.