Since the power transformer is an important kind of electric power equipment in power system, in this paper, comprehensive evaluation of power transformer are divided into three parts: power transformer operation status, fault diagnosis and repair strategies. Furthermore, the evaluation methods of comprehensive evaluation analysis are proposed, which means, on-line monitoring, the method of fault diagnosis and condition-based maintenance strategy decision-making method. Summarizing the research thought, the application conditions and the research progress of these methods. Finally, some open problems for comprehensive evaluation of power transformer in this area are introduced.