This application discloses a current differential protection data synchronization method of an AC line and a related device. The method includes: first judging the faulty phase of the three-phase line through the starting condition of the starting element; then using the sending end of the faulty phase to measure the voltage and related The line parameter calculation is the voltage change of the receiving end, that is, the calculated voltage; finally, the waveform matching can be performed between the target measured voltage before and after the starting element of the receiving end and the calculated calculated voltage, and the maximum value of the calculated waveform similarity can be obtained. The sampling time error between the AC lines on both sides, that is, the time error, the operation process is easy to execute, the calculation is simple, and the obtained data is highly reliable. In addition, the entire process of the scheme does not depend on the consistency of the data sending and receiving channels. Therefore, the present application solves the technical problem that in the existing channel-based data synchronization technology, channel multiplexing easily leads to inconsistency of transmission and reception channel delays, resulting in misoperation of current differential protection.