Abstract: In the wide-field and super high-resolution spaceborne Synthetic Aperture Radar (SAR), the traditional hyperbolic slant range model is no longer available, which is due to the variance of equivalent velocity in azimuth direction is able to cause azimuth defocus. For this problem, this paper proposes a new acceleration slant range model, which considers the azimuth variance of equivalent velocity. Based on this model, the corresponding signal processing and imaging method is given. Firstly, the azimuth variance of velocity is eliminated by azimuth resampling in the time domain. Secondly, the third-order and fourth-order error is eliminated in the 2D frequency domain. Finally, Range Migration Algorithm (RMA) is used to get the final image. The simulation results validate the effectiveness of the new acceleration slant range model and imaging algorithm.