Traditional differential protection is widely used in protected transmission lines because of its simple principle and high reliability. However, due to the inconsistency of the communication paths at both ends during the synchronous acquisition phase, the collected currents have differential, which reduces the reliability of the differential protection to a certain extent. Therefore, under the background of 5G communication technology, an adaptive differential protection based on transient direction suggests in this paper. The method improves the reliability of differential protection by changing the braking coefficient according to the transient direction on both sides of the line. The simulation experiment is performed by MATLAB / Simulink. When the external fault occurs, the differential protection device successfully identifies the differential current caused when the synchronous path is inconsistent, and ensures the reliability of the internal and external fault action mode.