Abstract: A phase-based method using a single channel SAR is proposed to estimate the radial velocity of ground moving targets unambiguously. Two-look operation in the range frequency domain and interferometry in the Doppler domain are done made to keep the phase meet the assumption of phase continuity. The lease squares linear fitting is used to estimate the slope between interferometric phase and Doppler frequency, and the radial velocity can be calculated by the slope. The proposed method possesses the advantage of being independent on phase wrapping. Compared with the single channel amplitude-based method, the method is able to provide greater precision and usefulness. The radial velocities of multi-targets can be estimated simultaneously in the Doppler domain. Experimental results validate the effectiveness of the proposed method.