Abstract: The transient current variation process of IGBT during switching includes the current rising process and the current dropping process. Due to the nonlinear characteristics of power devices and their close coupling with circuit parameters, the electromagnetic phenomena during the transient process are complex. The coupling law of voltage and current parameters in transient process is emphatically studied, and the influence of the coupling relationship on the operating characteristics of IGBT is analyzed. Firstly, the influence of parasitic PIN structure within IGBT and the collector-emitter voltage on the gate control model is analyzed. Secondly, based on the analysis of the gate control model, it is proposed that the fitting times of the collector current should consider the duration of the current variation process and the calculation scenario. Polynomial fitting of 2 or less times can approximate the waveform of the collector current and is sufficient for power loss analysis, but is not suitable for analyses of current variation rate and induced voltage. Moreover, the differences in the parasitic inductance calculation using the turn-on and turn-off waveforms are compared. The applicable range of calculating the parasitic inductance of the test circuit in different processes and the calculation method of the parasitic inductance in FWD packaging are proposed. Finally, the coupling relationship between the gate voltage and the collector-emitter voltage during the transient process is analyzed, and a state monitoring method of estimating the collector-emitter voltage with the gate voltage is proposed and experimentally verified.