Abstract: Porcelain insulators are widely used in power distribution lines, but they are susceptible to degradation during operation owing to long-term electromechanical stress and harsh outdoor environments. Infrared thermal imaging is an important live insulator degradation detection method. It has the advantages of convenient detection, safety, high efficiency, and non-contact operation. It has become an important method in power inspection. However, the thermal image characteristics of faulty insulators are not evident and cannot be recognized directly by the naked eye. Therefore, in this study, we first conduct a temperature field simulation analysis of porcelain insulators in distribution lines and then propose an infrared thermal image detection method for faulty insulators. A multi-scale template matching algorithm is used to locate and identify the insulators. The coordinate parameters of the insulator in the infrared image are obtained, the insulator is segmented and extracted by multi-scale template matching, and the temperature of the insulator is extracted by least-square linear fitting. Combined with the relevant standards and simulation analysis results, the differences in the temperature states among multiple insulators were compared using a similar comparison judgment method to detect faulty insulators.