<p>Marine thin plates are susceptible to welding deformation owing to their low structural stiffness. Therefore, the efficient and accurate prediction of welding deformation is essential for improving welding quality. The traditional thermal elastic-plastic finite element method (TEP-FEM) can accurately predict welding deformation. However, its efficiency is low because of the complex nonlinear transient computation, making it difficult to meet the needs of rapid engineering evaluation. To address this challenge, this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds. This method is based on the coupled temperature gradient-thermal strain method (TG-TSM) that integrates inherent strain theory with a shell element finite element model. The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis. This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation. The proposed method—particularly, the gradual temperature gradient-thermal strain method (GTG-TSM)—achieved improved computational efficiency and consistent precision. Furthermore, the proposed method required much less computation time than the traditional TEP-FEM. Thus, this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.</p>