In this paper, a novel spaceborne SAR imaging mode is proposed. In this mode, sensor illuminates the scene with different azimuth squint angles and obtains a series of sequential images. According to the working mechanism of the mode, the geometry model is built first. Based on the geometry model, the characteristics of signal are analyzed in detail, which reveals principle of velocity estimation. Moreover, combined with image formation processing algorithm, moving target velocity estimation method is present. Furthermore, some conclusions are drawn and discussed. Finally, simulation data and TerraSAR-X real data are used for verifying the validity of the method.