This paper analyzes the electromechanics of the spherical metal particles in AC gas-insulated lines (GIL) with a pragmatic test rig comprising coaxial cylindrical electrodes. Analysis on fluid resistance during the particle moving process is presented based on fluid mechanics as well as the kinetic parameters of the SF6/N-2 mixture. The interactive impacts between the particle and the conductor or the shell are also proposed based on collision theory of elastic mechanics considering random effects caused by the metal surface roughness. With the above aspects being included, a dynamic motion model for the spherical metal particles within AC GIL is established accordingly, and experimental studies are carried out to validate effectiveness and accuracy of the proposed model. Meanwhile, simulations are done regarding a real 220 kV AC GIL for further governance and verifications. The research observations indicate that, the applied voltage exerts an incremental effect on the maximum height of the moving particle, but won't affect the spread angle of the particle motion. Both the height and the spread angle of the particle's motion show inflection points with increased particle radius. On the contrary, the maximum height of the moving particle decreases with the increase of SF6 ratio and the gas pressure.