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Circular synthetic aperture radar (SAR) imaging on the geosynchronous orbit is an innovative SAR imaging mode, which can produce high-resolution three-dimensional (3D) images and offer 24-h continuous surveillance of a broad area. In this paper, we use the geosynchronous circular synthetic aperture radar (GEOCSAR) to efficiently produce high-resolution 3D surface displacement maps by repeat pass interferometry. The coverage areas with GEOCSAR imaging can be mapped from different view directions; thus, a 3D displacement can be provided daily. First, we derive the connection between the GEOCSAR interferometric phase and the surface deformation for analytically interpreting its capability to resolve the three components of the deformation. Then, to retrieve the three components of the deformation, a retrieval matrix is deduced. Furthermore, analyses of the errors in the observation phase vector and retrieval matrix are described, and the way these errors propagate into the deformation vector is modeled. To reduce the errors of the deformation measurement, the retrieval matrix is optimized by choosing appropriate parameters and making the condition number of the matrix minimal. Finally, the simulation results validate the correctness of the analysis, and the 3D retrieval deformation is presented with three subapertures and shows an improvement of accuracy when the optimal retrieval matrix is used.