Abstract: During the monitoring of transformer core earthing signals (CES), very fast transient overvoltage (VFTO) impulses have been recorded many times, which provides a new way to detect the VFTO impulse. In order to research the way of VFTO coupling to CES, and to analyze the VFTO signal features in CES, firstly, the generation of VFTO is simulated and analyzed. Secondly, the high-frequency hybrid model of the winding is established, and the transmission process of VFTO in the winding is analyzed. Lastly, the core high-frequency capacitance model is established and united with the previous model for simulation to analyze the process of VFTO-pulse generation in CES. Moreover, the VFTO-pulse features are summarized and the VFTO-pulse knowledge is established. Meanwhile, a comparative analysis of the opening process of a disconnector in a hydropower station is carried out by simulation. The simulation waveform and the field recording waveform are basically the same. The above studies show that VFTO is transmitted along the line and coupled through the capacitances on the winding, and then coupled to CES through the capacitance between the winding and the iron core and inside the iron core to generate VFTO-pulses, which possess the characteristics of gradually increasing amplitude and gradually sparse distribution in the opening process of the disconnector, but they are completely opposite in the closing process. Through this study, the whole process of VFTO coupling to CES is obtained, the key characteristics of VFTO-pulse in CES are summarized, and then the feasibility of detecting VFTO impact by CES is proved.