A ring beam and its retaining structure are regarded as an elastic ring and an elastic thin cylindrical shell, respectively. In this study, based on the deformation compatibilities between the ring beam and cylindrical shell, an analytical solution for the deformation of a retaining structure of a circular deep foundation pit with any number of elastic ring beam supports is obtained. Based on the verified rationality and reliability of the analytical solution, this study compares the differences in deformation and internal force distributions of the retaining structure of a practical circular deep foundation pit with rigid and elastic ring beams, respectively. In addition, influence of parameters including bottom boundary conditions of the retaining structure, elastic modulus, size, number, and position of the ring beams on the deformation and internal force distributions of the retaining structure are studied. Results show that, compared with the internal force changes to the retaining structure with a rigid ring beam, those to the retaining structure with an elastic ring beam are relatively small. In addition, changes to the elastic modulus and size of the ring beam are found to have a significant effect on the deformation and internal forces of the retaining structure above the excavation surface of the foundation pit. However, they have little influence on the deformation and internal forces of the retaining structure below the excavation surface. These results provide a theoretical basis and guidelines for the design of a retaining structure of a circular foundation pit.