The possible causes of the oil level abnormity were analyzed for the main transformer oil level abnormal defects,combined with the actual oil level,showed oil level and temperature-oil level curve.The length of pointer-type oil level swing-rod was calculated.The capacity of oil conservator was calculated and analyzed,and results show that it should be at least 10% of the body oil volume of main transformers.Defects and errors of existing main transformers were pointed out,and treatment measures and operational maintenance suggestions were put forward,which provides a reference for the main transformer acceptance and maintenance work.