In this paper, we propose a novel algorithm for SAR ground moving target imaging (SAR/GMTI) and motion parameters estimation (MPE) in consideration of Doppler ambiguity. This algorithm involves the keystone transform (KT) and the modified second-order keystone transform (MSKT), Radon transform (RT) and Fractional Fourier transform (FrFT). With this algorithm, the fast moving targets can be focused well and the motion parameters can be es- timated accurately even in situation of Doppler ambiguity. The effectiveness of the proposed algorithm is demonstrated by processing the simulated airborne SAR data.