Abstract: Transformers are key equipment for achieving voltage transformation in the power system, and their safe and stable operation directly affects the safety of the entire power system grid structure. This article elaborates on the inspection and treatment of oil leakage in the 220 kV side bushing of a main transformer, conducts dielectric loss and capacitance tests on the bushing, and analyzes the disassembly inspection. Finally, the main cause of the sealing failure of the inner sealing ring of the bushing is determined, and subsequent rectification suggestions are proposed.