A discharge accident of the electromagnetic unit of 110 kV capacitive voltage transformer（CVT）is introduced in this paper. It is judged throughout such analysis as appearance inspection，oil spectrum test，electrical test and internal disassembly of the electromagnetic unit of the faulty CVT that the accident is caused by the lax seal due to foreign objects at the flange connection between the capacitor unit and the electromagnetic unit. The moisture penetrating into the electromagnetic unit causes the insulation to become damp，thus reducing strength and resulting in discharge. The fault reflects the deficiencies in the overall testing and foreign object detection methods during the production stage of the equipment，and specific sug-gestions and preventive measures are proposed for safe operation of CVT in the future.