Abstract: The solder layer of insulated gate bipolar junction transistor（IGBT）is selected as the research object. Based on the traditional Cauer model,the dual-branch Cauer model considering chip-copper terminal heat flow branch was proposed. The temperature of copper terminal exposed outside the IGBT module and the temperature of IGBT module baseplate were measured by optical fiber temperature sensor to obtain the IGBT chip junction temperature. By analyzing the changes of chip junction temperature,copper terminal temperature and baseplate temperature,the aging position of the solder layer is accurately located,the chip solder layer aging and baseplate solder layer aging is effectively distinguished.