Abstract: For the multichannel synthetic aperture radar ground moving target indication system with the capability of high resolution wide swath imaging (HRWS SAR/GMTI), the echoes of each channel suffer from Doppler frequency ambiguity, which leads to sever velocity ambiguity during parameter estimation. Concerning this issue, a high-accuracy unambiguous estimation method of radial velocity is proposed. Firstly, since the space-time spectrum of moving targets echoes is unambiguous in space dimension after chirp Fourier Transform (CFT), it avoids the influence of ambiguous components while adaptive filtering in space domain, thereby reducing the number of necessary channels. Afterwards, to obtain the high accuracy unambiguous radial velocity, the spectrum estimation and Radon Transformation are employed to estimate the baseband radial velocity and ambiguity number separately. With regard to the scene that there are several moving targets emerge from one range bin, some simulation experiments are taken to demonstrate that the proposed algorithms is highly effective.