Abstract: This paper investigates the problem of fast moving target indication in synthetic aperture radar and ground moving target indication (SAR-GMTI). In order to improve the detection probability, the range walk caused by the velocity component corresponding to baseband Doppler centroid can be corrected by Keystone transform, and the residual range walk is proportional to the Doppler shift which equals to several pulse repetition frequencies (PRF), which can be corrected in range compressed azimuth time domain. The SAR image of moving target can be formed with azimuth matched filtering after range walk correction. Since the range walk caused by high speed is not ambiguous, thus we can exploit its information and resolve PRF ambiguity, and at last get the unambiguous velocity of target. Measured data processing illustrates the proposed method is effective.