Abstract: The detection of gas content in insulating oil of transformer is very important for the safe and stable operation of large transformers. First, if the gas content is too high and exceeds the dissolving capacity of insulating oil (generally 10%), the dissolved gas in insulating oil will precipitate in the form of bubbles, which will reduce the overall insulating performance of insulating oil and cause partial discharge in the oil. Second, when the gas content exceeds the standard, the air in the environment is generally absorbed into the transformer, and the oxygen in the air will react with insulating oil and materials to accelerate the insulation aging process of the transformer and shorten the service life of the transformer; Third, the gas precipitated from the insulating oil will continuously gather in the gas relay, which will cause the misoperation of the gas relay in severe cases and lead to the tripping of the main transformer. This paper summarizes the experience in the process of the gas content exceeding the standard in the main transformer of 500kV Yuxi Transformer, and describes in detail the inspection and treatment steps and cause analysis of the gas content exceeding the standard in the transformer, which has certain reference significance for the treatment of the gas content exceeding the standard in the same type of transformer.