Abstract: The occurrence of transformer deflagration accidents mostly originates from its internal insulation defects of partial discharge, and gradually develops to spark discharge and arc discharge, causing huge economic losses. The study of internal discharge signal characteristics and its rapid detection methods to ensure the safe and reliable operation of power transformers is of great significance. Scholars at home and abroad have carried out a lot of research work around the internal insulation defects of transformer discharge characteristics and detection methods. This paper summarizes the research results from aspects of partial discharge, spark discharge, and arc discharge three stages, and summarizes and analyzes the physical and chemical characteristics of different discharge development stages such as pulse current, electromagnetic wave, sound, light and chemical products, etc. At the same time, this paper outlines the detection methods based on different signals and the requirements for detection equipment, compares the advantages and disadvantages of different detection methods, and finally puts forward research prospects for the development and detection of insulation defects in transformer discharges. Finally, the research outlook for the development of transformer insulation defect discharge detection is put forward. This paper has guiding significance for further in-depth research on the feature extraction of discharge signal in oil, rapid detection and active protection technology of transformers.