This paper presents an efficient imaging algorithm for missile-borne SAR. In the course of missile's diving flight, it is difficult to use the traditional imaging principle because of the strong coupling between range and azimuth signal. Through the fourth order range model, the echo model is established and the two-dimensional point target spectrum is derived by the method of series reversion. Then, the corresponding range and azimuth match filtering functions are given. Finally, simulation results demonstrate the accuracy and validity of the proposed algorithms.