Abstract: Electromagnetic topology (EMT) technology is an effective method for solution of the transient response of complex systems, and it has been widely used to analyze the response behavior of transmission line networks under external excitation. However, in the EMT modeling of the transmission line (TL) networks, the incomplete decoupling of the separation lines at the ideal junction will cause the generation of the inevitable errors in the calculation results. In order to clarify the mechanism and key influencing factors of the error, this paper starts with the analysis of BLT equation and determines the origin of the error. Furthermore, the influence of several key factors such as separation angle, gap, height and length of separation line on modeling accuracy is analyzed by the transient results of crosstalk voltage. The work of this paper reveals the inherent errors of EMT modeling methods, clarifies the shortcomings of this technology, and provides useful references for further optimization in the future.