Abstract: Transformer bushing has the functions of supporting drainage wire and extending insulation distance,and it is an important current carrying element of transformer,whose sealing performance,insulation strength and thermal stability will directly affect the stable operation of transformer. Abnormal chromatographic data of insulating oil in bushing and the excessive dielectric loss is common faults of bushing due to poor sealing. A case of serious oil shortage in bushing caused by improper operation of oil extraction is analyzed,which results in excessive dielectric loss and abnormal oil chromatographic fault.