Abstract: Transformer oil is susceptible to contamination by various particulate impurities during practical use, posing a potential threat to its insulation performance. While many studies have examined the movement of fibers, metals, and carbon particles, research on rubber particles remains insufficient. Rubber particles typically originate from aging rubber seals and insulating materials within the transformer, which deteriorate and fracture over time, creating fine particles suspended in mineral oil. A testing platform is established for measuring the breakdown performance of mineral oil under alternating current(AC). Utilizing high-speed photography and shadowgraphy techniques, the motion characteristics of rubber particles in mineral oil and their impact on breakdown phenomena are investigated. Additionally, the evolution of the behavior of rubber particles is analyzed from individual movement to collective dynamics through fluid-field coupling simulations. The results indicate distinct motion trends for particles outside the electrode gap, significantly influenced by their initial positions and sizes. In contrast, rubber particles within the electrode gap exhibit reciprocating motion, ultimately aggregating into an increasingly thicker wall-like structure until breakdown occurs. This research provides valuable insights into understanding the impact of impurity particles on the insulation performance of transformers.