A method for estimating the junction temperature on-line on an insulated gate bipolar transistor (IGBT) power module, including the following steps. Estimate the junction temperature by the temperature sensitive electrical parameter method, set the space thermal model of the extended state, and apply the Kalman filter to the junction temperature estimation. The temperature sensitive electrical parameter method estimates the junction temperature of the IGBT power module in real time, selects the IGBT conduction voltage drop VCE(ON) as the temperature sensitive electrical parameter, and provides a VCE(ON) on-line measuring circuit. The power loss of the diode and IGBT and the estimated value of junction temperature obtained by the temperature sensitive electrical parameter method are taken as the input of the Kalman filter, and measurement noise and process noise are considered to obtain an optimal estimated value of junction temperature.