For the problems of massive calculation errors and weak anti-interference ability in traditional differential protection. A novel pilot protection strategy for multi-terminal flexible DC lines, based on amplitude matching of the current’s forward and backward traveling waves, is proposed. First, the distinct features of the fault current’s forward and backward traveling waves at the line terminals during both internal and external faults are analyzed, further based on the time-frequency domain relationship between the forward and backward traveling waves of the fault current at both ends of the line under external faults, the calculated and measured waveforms are obtained. Second, the amplitude matching principle and Euclidean distance algorithm are used to construct the main protection criterion, and integrating the initial criterion with the pole selection criterion leads to the development of a pilot protection method. Finally, the PSCAD/EMTDC platform is used to establish a four-terminal flexible DC network for simulation verification. The results obtained from the simulations demonstrate that the protection method proposed can swiftly and dependably detect faults occurring both inside and outside the designated zone, and withstand 300 Ω transitional resistance and 30 dB Gaussian white noise.