Abstract: The welding deformation during the welding process of spherical cap structure is a very important guideline on the structural safety.In order to guarantee the reliability of welded spherical cap structure and estimate the welding deformation accurately, it is necessary to carry through the numerical simulation analysis of welding deformation on spherical cap structure.The temperature field and structural deformation during the welding process were numerically simulated with a welding program, which was developed based on the large FEM software ABAQUS.Then the simulation results were analyzed and compared the correlative theoretical results with the experimental results.The contrasted results show that the numerical simulation results correspond basically to the theory results, thus the engineering requirements are satisfied.Based on these studies, 3D FEM numerical simulation of the welding process on the spherical cap structure was presented.And the variation of welding deformation with the plate thickness of spherical cap structure, welding groove shape and welding sequence was obtained, which provides the reliable foundation for controlling the structural welding deformation.