The Polar Format Algorithm (PFA) mainly uses interpolation algorithm in the Inverse Synthetic Aperture Radar (ISAR)imaging algorithm to solve the problem of cross-range migration of scattering points.The selection of the interpolation method determines its imaging efficiency and computing speed.In this paper, an interpolation method along the line of sight of radar is proposed.The geometric model of ISAR target with large rotation angle is established, the precise interpolation form of azimuth direction is obtained by theoretical derivation, and azimuth resampling is carried out for the deformation caused by non-uniform sampling.Simulation results show that compared with the traditional interpolation algorithm, it has the advantages of faster operation speed and better focusing performance.