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A novel procedure is proposed to estimate the two-dimensional (2-D) velocity parameters of moving targets from single-channel synthetic aperture radar (SAR) data in a long-time coherent integration for motion compensation. First, the SAR data is divided into several sub-band data by sub-aperture decomposition, since target motion may be changing in the whole long-time aperture, so that the velocity estimation for each sub-band can be performed respectively. Then, the range walk correction is carried out via Doppler centroid analysis based motion estimation and compensation, by which the energy of the moving target is concentrated into a single range cell. This processing is especially advantageous to the following exact Doppler parameter estimation. Finally, the fine 2-D motion parameters are estimated based on mismatched compression simultaneously. Compared to conventional algorithms with a time-consuming searching process, the 2-D velocity estimation of moving targets can be carried out using this algorithm more efficiently, and the SAR image can be well focused and right located after further motion compensation. Experimental results for numerically simulated SAR images demonstrate the effectiveness of the proposed technique.