Abstract: The Doppler parameters of missile-borne SAR received signal vary much with slant range due to missiles high speed and non-ideal movements. Thus applying the classical wave-number domain algorithm can hardly achieve high precision for missile-borne SAR imaging processing. This paper proposes a modified wave-number domain algorithm based on the classical one to meet the demand of high resolution and wide swath for missile-borne SAR imaging. Azimuth compression is implemented in the range time domain or range space domain instead of two dimensional wave-number domain in which it is carried out for the classical algorithm. And Doppler parameters can not correspond to the variation of slant range in the two dimensional wave-number domain. Consequently the modified approach can eliminate the phase error brought by using the same Doppler parameters for the classical algorithm. Simulation result illustrates the validity of the approach.