Abstract: GIS equipment often suffers from lightning overvoltage during operation, and the equipment actually bears the effect of AC superimposed lightning impulse voltage. At this time, high amplitude impulse voltage excites linear metal particles to start moving and generate partial discharge, seriously threatening the safe operation of GIS equipment. Therefore, this paper establishes an AC superimposed lightning impulse voltage test system, which combines partial discharge measurement and optical image observation methods to study the partial discharge characteristics and motion behavior of linear metal particles in SF₆ gas under AC superimposed lightning impulse voltage. Combined the the partial discharge characteristics and motion behavior of linear metal particles, the motion mechanism and partial discharge mechanism of linear metal particles under AC superimposed lightning impulse voltage are analyzed. The results show that the superimposed voltage can stimulate the movement of linear metal particles; however, after the action of lightning impulse voltage, there is no obvious partial discharge signal immediately. Instead, a continuous partial discharge begins to occur after a delay time, which is related to the physical size and number of the defect. In addition, jumping motion through the electrode is more likely to occur during the subsequent continuous discharge process. The research work in this paper is conducive to a deeper understanding of the motion characteristics of metal particles in actual equipment and the process of causing partial discharge, and has guiding significance for equipment operation and maintenance analysis and equipment manufacturing improvement.