The polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) is influenced by wavefront curvature error. The error introduced will cause the missile borne SAR image edge blur and geometric distortion seriously. The previous wavefront curvature compensation methods are all assumed that the height of the radar is constant. These compensation methods cannot be directly applied to the case of missile borne SAR where the platform always has large dive angle. The application range of wavefront curvature error compensation method is restricted greatly. In this paper, the precise expression of wavefront curvature phase error in the frequency domain of missile borne SAR is derived. After image domain post-processing steps, the problems of distortion and defocus of PFA image in the missile borne SAR are solved effectively. This method further improves the precision of wavefront curvature compensation. At last, the correctness of formula and method is verified by simulation.