Ground moving target imaging (GMTIm) is essential for Squint SAR in modern military applications. However, the GMTIm processing becomes more complex and difficult than that in the broadside SAR due to the squint angle. In this paper, we propose an algorithm for squint SAR GMTIm and motion parameters estimation (MPE) with the Keystone transform (KT). With this algorithm, the target's motion parameters can be estimated accurately and thus the moving target can be well focused. The effectiveness of the proposed algorithm is demonstrated by processing the simulated SAR data.