Abstract: The article introduced the oil leakage defect of the 500 kV transformer respirator, and introduced the on-site inspection, the analysis of the causes of defects, the temporary processing measures and the power outage maintenance process. The power outage inspection confirmed that the damage to the oil storage tank capsule caused transformer oil to flow into the capsule. After the oil level rose, the capsule was compressed, and the oil was discharged from the respirator outlet through a breathing tube, resulting in respirator oil leakage. Finally, suggestions were put forward to prevent capsule damage, in order to improve the safety and reliability of the capsule and ensure the safe operation of the transformer.