Abstract: Oil-immersed capacitive high-voltage bushing is widely used in large transformers,which undertakes the functions of carrying current,insulation and sealing. Based on an inter-turns short-circuit fault of a 220 kV transformer,which happened after a series of earthquakes,the testing detection,disassembly inspection and bushing structure analysis are carried out. The results show that the fault comes from the unreasonable design of the sealing structure of bushing,which fails in special conditions.