The fault characteristics of inverter AC transmission lines in AC-DC interconnection networks are quite different from those of pure AC systems. The protection scheme of traditional AC transmission lines is no longer suitable for inverter AC transmission lines. First， based on the different topological structures of the inverter AC transmission line when the fault occurs inside and outside， the expressions of the first traveling wave of the down-mode fault component current are derived， respectively， and the difference of the first traveling wave characteristics of the AC transmission line when the fault occurs inside and outside is clarified theoretically. Then， wavelet transform mode maximum method and Levenberg-Marquardt algorithm are used to extract the curvature radius of the first traveling wave， and a high-reliability single-terminal protection scheme is constructed by using the curvature radius of the first traveling wave to identify the fault region. Finally， the AC-DC interconnection network model is built in PSCAD/EMTDC， and the protection scheme is verified by MATLAB. The simulation results show that the proposed protection scheme is fast and effective， has high reliability， strong resistance to transition resistance， and good anti-noise ability.