Abstract: An accurate real-time online detection for the internal junction temperature of IGBT is one of the prerequisite conditions for the normal, reliable and long-term operation of the electromagnetic induction heating power supply system on the continuous casting and rolling line. The paper adopts a chip based on the principle of optically isolated linear optocoupler technology, combined with the voltage acquisition at both ends of the NTC thermistor inside the IGBT and the conversion and processing of V/I and I/V signals, designed a signal acquisition circuit for real-time detection and calculation of the internal junction temperature of a single IGBT, and based on the design concept of unit modularization and master-slave distributed acquisition system, design a real-time and independent monitoring system of all IGBT junction temperatures in MW-class high-power induction heating power supply with wide power range. The results of experiments and practical applications show that, the IGBT internal NTC thermistor temperature acquisition and detection system based on the principle of optically isolated linear optocoupler can meet the performance requirements for real-time monitoring of IGBT junction temperature in high-power induction heating systems, and the system has been successfully integrated into the independently developed MW level high-power induction heating power supply control system.