It is difficult to detect a target with a low speed since it may drop into main lobe clutter in both time domain and frequency domain. A multi-channel SAR-GMTI algorithm was proposed to solve this problem which can suppress the clutter with Displaced Phase Center Antenna (DPCA) estimate the parameters of moving target with Fractional Fourier Transform (FrFT) and acquire the scene image by constructing the azimuth compression function. The proposed approach takes full advantages of the abundant information of three channels makes use of the ideal clutter cancellation capability of DPCA technique and the fine energy focusing ability of the FrFT which can estimate the parameter of moving target accurately including radial acceleration. The results of the simulation indicate the effectiveness of the methods.