Abstract: The basal principles of Differential Interferometric Synthetic Aperture Radar (D-InSAR) were described briefly in this paper. Taking an old goaf in Xuzhou as an example, the deformation field of the surface was obtained by processing radar image data with two-track differential interferometric. Studies have shown that the D-InSAR technique can be applied to monitor a large area of the old goaf residual deformation.