Abstract: With the advantages of rapid action and strong anti-interference, the optical fiber current differential protection has been widely used as the main protection for the transmission lines in power systems and is used in the form of double protection for 220-kV transmission lines in a real power system. However, it is happened recently that the operation of the double protection is inconsistent with each other, which needs the technicians to draw their attention. In this paper, the in-depth analysis on this case is conducted from the aspects of protection principle, fault waveforms and TA selection to explore the features and causes of the protection action and find the preventive measures. The results indicate that this case is quite typical and can be regarded as the factor for type selection with TA. The corresponding preventive measurements can be provided for operators and maintainers to deal with the similar cases quickly and easily.