Abstract: Transformers are the primary core equipment of substations, and their operational stability directly impacts the safe and reliable power supply of the entire electrical system. As critical foundational components of transformers, high-voltage cable-through bushings rarely cause forced outages of main transformers due to sudden oil leakage. An in-depth inspection and analysis of an unplanned outage incident triggered by sudden oil leakage in a 110 kV transformer′s high-voltage cable-through bushing revealed scattering in the tensile strength of the raw material used for the bushing′s central conductive tube. Ultimately, it was identified that the bushing′s mechanical properties failing to meet design requirements constituted the root cause of this incident. Based on these findings, considerations and improvement suggestions are proposed for similar transformers during construction, operation, and maintenance phases.