To investigate the stress distribution in 550 kV Gas-Insulated Lines (GIL) three-pillar insulators, a stress simulation model was developed using COMSOL Multiphysics, a finite element simulation software, based on a typical 550 kV GIL insulator structure. This model allowed for the simulation of the insulator's behavior under gravity and transport conditions, including a principal stress analysis under both axial and radial loads. The findings revealed that uneven stress distribution results in micro air gaps or cracks, affecting the mechanical properties and degradation of the insulators. Specifically, in the transported state, the maximum stress, at 64.9 MPa, was observed at the connecting cylinder's edge, accompanied by a deformation of 68 μm. Moreover, the insulator's damage under radial load is determined by the tensile strength of the interface's curved epoxy, while axial load damage relies on the interface's shear strength.