Given the effect of access of the DC system, the fault characteristics of the frequency offset on the AC side and the poor adaptability of the superposition principle may lead to the possibility of mis-operation or refusal of the conventional pilot protection based on the power frequency fault component. On the basis of the parameter identification idea, the line fault of the AC transmission line of an AC/DC hybrid system is analyzed, and a method based on the similarity of the resistance model is proposed. If the fault meets the resistance model, it is determined as an internal fault, and if it does not, it is determined as an external fault. Protection criteria are proposed. The protection scheme adopts the full time-domain, solves the problem that the superposition principle is not applicable, and overcomes the influence of frequency offset on protection. Simulation results show that the protection scheme can identify faults accurately and quickly. The protection scheme based on the similarity discrimination of the time-domain full resistance model is adapted to the AC/DC hybrid system. This work is supported by National Natural Science Foundation of China (No. 51877185).