In order to minimize and uniform radial deformation in the oil cylinder of an ultra-high pressure double-stage hydraulic bolt tensioner during operation. Finite Element Analysis (FEA) was deployed to conduct comprehensive simulation calculations. These simulations predicted that the increase in piston position and oil pressure would cause an increase in both the radial deformation of the tensioner cylinder and piston deformation, notably with substantial circumferential disparities in the lower cylinder.Optimization involved modifications to the structure at the top of the lower oil cylinder. After an optimal parameters determination, a new three-dimensional tensioner model was reconstructed for simulation. Results indicated that radial deformation decreased by 18% relative to the original structure.In conclusion, the experimental outcomes confirmed the rationality and effectiveness of the optimized structure. Repeated pressure tests showed reduced internal leakages in the optimized structure, and the uneven radial deformation phenomenon was also improved. The study not only demonstrates the importance and reliability of FEA in tensioner design but also provides an accurate strategy for optimizing product structure and expediting new product development.