Abstract: The continuous improvement of global regulations on fluorinated gases propels the development of vacuum circuit breakers towards higher voltage levels. The insulation strength of the vacuum interrupter, a core component, must meet elevated requirements. A 252 kV vacuum interrupter with a multi-stage suspended shielding structure is investigated. An electric field simulation model is established, and insulation strength analysis is conducted from both the internal and along the surface of the ceramic shell. The analysis reveals issues such as concentrated electric fields at the triple junctions, uneven voltage distribution along the ceramic shells, and non-uniform electric field distribution along the shell's surface. Addressing these concerns, a capacitance equivalent circuit model is proposed to analyze the principles of electric field potential distribution. Based on this analysis, an electric field optimization scheme suitable for multi-stage suspended shielding vacuum interrupter is presented. The optimization is applied to the vacuum interrupter, and a comparative analysis of the electric field before and after optimization is conducted. Results indicate a 77.3% and 77.2% reduction in electric field intensity at the the triple junctions on the dynamic and static ends, respectively. The voltage distribution along the ceramic shells becomes more uniform, and the maximum tangential electric field along the ceramic shell's surface on the static end decreases by 38.3%. The proposed optimization significantly enhances the insulation performance of the vacuum interrupter. The proposed electric field optimization scheme can serve as a reference for the design of electric field optimization in vacuum interrupter with multi-stage suspended shielding structures.