Abstract: As a more general CSAR imaging mode, spiral trajectory SAR reduces the limitation that the platform must be at the same height plane, improves the maneuverability of the platform, and has high research value. The Polar Coordinate Format Algorithm (PFA) for Circular Synthetic Aperture Radar (CSAR) imaging corrects the wavenumber quadratic phase error by a two-step phase compensation operation, which improves the imaging scene size limitation caused by the plane wave hypothesis. Since the slant range of the spiral trajectory SAR has been changing, the quadratic phase of the wave number becomes more complicated and difficult to compensate. The algorithm firstly aligns the spiral SAR echo data in a distance direction, and then based on the two-step compensation operation in the PFA algorithm. A new phase compensation function and compensation strategy are established, which accurately compensates the secondorder phase error of the wave number in the geometric imaging of the spiral trajectory, and obtains a large effective imaging range. Finally, the point target simulation verifies the effectiveness of the algorithm.