Abstract: In the field of shipbuilding and repair, thermal deformation readily occurs during the cutting of full-circle ends of large hull sections, compromising structural accuracy and subsequent construction processes. To control the effect of flame cutting on the thermal deformation of full-circle ends, a surface Gaussian heat source model, a volumetric heat source model, and the finite element “birth-death” element technique were employed to predict the evolution of temperature, stress, and displacement fields during the four stages of actual flame cutting process. Based on these predictions, a method for controlling cutting-induced thermal deformation by installing stiffening structures in the near-seam zone was proposed. The diameter deformation at each measurement point on the full-circle end of the hull section after cutting was measured using a laser tracker and compared with the corresponding radial displacement values predicted by the finite element model. The maximum relative error was 9.82%, verifying the reliability of the flame cutting thermal deformation prediction model. A comparative analysis was further conducted using finite element models with and without stiffening structures. The results indicated that longitudinal reinforcement plates in the near-seam region can effectively reduce the radial displacement at each measurement point on the full-circle end after cutting, with an average reduction of 0.12 mm. The proposed model and method can provide an effective numerical analysis tool for predicting and controlling flame-cutting deformation of full-circle ends in large ship sections, significantly reducing the cost of full-scale ship testing.