An improved nonlinear chirp scaling (NLCS) algorithm for dechirped missile-borne synthetic aperture radar was proposed. The key step is to use an improved NLCS operation to equalize azimuth frequency modulation rate after linear range walk correction, secondary range compression, and range compression. By adopting a higher-order approximation, the image has better accuracy and less distortion. Validity of the algorithm is demonstrated using simulated and real datasets. Moreover, the whole procedure only consists of fast Fourier transform and complex multiplication, which means easier implementation and higher efficiency.