Abstract: This study investigates the corrosion-induced failure mechanism of spring finger contacts in valve-side bushings of ultra-high-voltage（UHV） converter transformers under oil-immersed conditions through on-site disassembly analysis and simulated experiments. Characterization techniques including SEM, EDS, and XRD were employed to analyze failed contacts, revealing copper sulfide（Cu₂S） as the predominant corrosion product. Notably, the surface Ag content sharply decreased from 92.6% to 7.6% with increasing corrosion severity. Insulating oil composition analysis combined with high-temperature corrosion experiments demonstrated that elevated temperatures and dibenzyl disulfide（DBDS） concentration synergistically accelerate degradation. At 250 ℃, a dense Cu₂S layer formed within merely 3 days, with corrosion rates exhibiting significant positive correlation with DBDS concentration. These findings provide critical theoretical foundations for enhancing UHV equipment reliability and advancing domestic manufacturing of corrosion-resistant spring finger contacts.