Abstract: Due to the change of operating frequency and the control mechanism of flexible low-frequency converter station, the fault characteristics of flexible low-frequency transmission system and its influence on protection principle are complicated. In order to analyze the applicability of fault component protection principle in flexible low-frequency transmission system, a double-terminal low-frequency transmission model with fault current limiting as fault control strategy is established based on the control architecture of flexible low-frequency converter station. After considering the control characteristics of the system when three-phase fault occurs in the line, the impedance characteristics of low-frequency fault component in different situations are analyzed, and the quantitative calculation formula of low-frequency equivalent impedance is deduced, and then the influence mechanism on traditional fault component protection components is analyzed theoretically. Finally, a double-terminal low-frequency transmission model is built on PSCAD/EMTDC platform to verify the theoretical analysis. The research results show that the flexible low-frequency transmission system can reduce the protection range of fault components and even completely fail the protection components under certain fault conditions, which has a certain reference for the development of relay protection research in low-frequency systems.