Abstract: The safe and stable operation of transformers plays a crucial role in the distribution of electrical energy and the smooth implementation of voltage conversion in the power system. Therefore, fault diagnosis of transformers is extremely important. Firstly, the fault mechanism and common fault types of transformers were elaborated. Secondly, a detailed analysis was conducted on various traditional and existing transformer fault diagnosis methods, pointing out the problems that transformer fault diagnosis technology needs to solve. Finally, the future research focus and development trend of transformer fault diagnosis are proposed, providing a certain reference for transformer fault diagnosis.