Abstract: In this paper, the coherency characteristics of a 100% converter-interfaced generation power system is studied, which is important for understanding the interaction patterns and stability characteristics of different converter-interfaced generation through the grid. After a large disturbance in the conventional synchronous machine system, the units usually have a relatively constant mutual sway pattern, but it is not clear whether the converter-interface generation has a similar pattern. At present, the widely connected grid-following converters exhibit current source characteristics and infinite internal impedance, so the electrical distance analysis method based on transfer impedance is no longer applicable. This paper first analyzes the deficiencies of the traditional synchronous machine system coherency analysis method. The transfer coefficient and its calculation method are then proposed based on the concept of transfer impedance, which provides more physical insight to analyze the system coherency and stability. Finally, the IEEE 39-bus 100% converter interface power supply power system is analyzed by constructing a transfer coefficient matrix, and the simulation results verify the accuracy and rationality of the proposed method. The proposed transfer coefficient solves the problem of measuring the electrical distance from somewhere in the system to the converter-interface generation and provides references and considerations for a more in-depth study of the 100% converter-interface generation power system in the future.