The ordinary SAR imaging algorithms are inapplicable to missile-bo-rne SAR due to the high speed dive and high-squint of missile. Aiming at this problem, this paper firstly sets up the model of echo and analyses of two-dimensional spectrum. By using azimuth nonlinear chirp scaling (NLCS) based on variable decoupling, an imaging algorithm for missile-borne SAR is proposed.It can effectively compensate the scene with longitudinal and transverse Doppler shift and improve the focusing quality while it can also simplify the geometric image correction operation. Simulation results are provided to confirm the effectiveness of the proposed algorithm.