Abstract: The ion thruster grid components are prone to unexpected electric breakdown, which not only affects the working stability and the reliability of the ion thruster, but also seriously affects the thruster’s grid components and power supply, and may even lead to its failure. This paper analyzes the breakdown characteristics and the mechanism of unexpected electric breakdown based on the obserbations in the ion electric propulsion test. On this basis, the different types of electric breakdown and their harmfulness are discussed. Finally, recommendations are proposed for the follow-up research of the electric breakdown of ion thrusters.