The transmission delay and interference signal of traveling wave directly affect the reliability of current mutation protection based on amplitude ratio DC transmission line. In order to solve this problem, this paper proposes to increase the longitudinal current difference as the starting criterion. The polarity criterion is constructed by using the current sudden change at both ends, and a new protection criterion is constructed based on the polarity comparison. Furthermore, in order to solve the delay problem of traveling wave transmission, the delay mechanism is analyzed in detail, and an error correction scheme is proposed to compensate the full delay in normal and out of the loop faults. In order to solve the DC characteristics of bipolar harmonics, the electromagnetic coupling between lightning and high-frequency pulse interference signals, Chebyshev window filter are adopted to get a better signal extraction results. Through the simulation of PSCAD/EMTDC, the protection scheme has simple principle, high reliability and low sampling rate. The result shows that the scheme has strong resistance to excessive resistance. This work is supported by National Natural Science Foundation of China (No. 51607106).