The invention provides a method and a system for calculating the transient junction temperature of an IGBT (Insulated Gate Bipolar Translator) module. The method comprises the steps of: acquiring circuit state information, loss parameter and internal thermistor voltage drop information; calculating power module loss according to the circuit state information and the loss parameter, and calculating substrate temperature according to the internal thermistor voltage drop information of the module; according to the temperature information provided by internal chips and the internal thermistor of the module as reference temperature, in consideration with thermal coupling between the internal chips of the power module at the same time, establishing a simpler IGBT module thermistor network model, and calculating a junction temperature rise according to the power module loss and the thermistor network model; and calculating the transient junction temperature according to the substrate temperature and the junction temperature rise, thus realizing on-line acquisition of the transient working junction temperature of the IGBT. By sufficiently utilizing the existing thermistor resource inside the power module, a junction temperature measurement system based on a power module electro-thermal coupling model is established, so that accurate power device junction temperature information is provided for security operation and health management of a converter system.