Space-time adaptive processing (STAP) is an effective method to suppress ground clutter and extract moving targets in the Multi-Channel SAR (MSAR) system. The space-time two-dimensional filter weight is decided by the evaluation of the clutter covariance matrix. From the MSAR echoes model, a method of raw-data simulation in the frequency domain by two-dimensional FFT is proposed and the evaluating of MSAR clutter space-time covariance matrix is made. The simulation result shows that the data produced by this method retain the reality of MSAR space-time clutter characteristic with lower computational complexity.