Existing transmission line differential protection is designed based on an optical fiber channel. It has high channel requirements which limit the popularization and application of dual channel and three route. In addition, the existing differential protection does not have the ability to identify inconsistent channel routing delays, resulting in the risk of differential protection misoperation. This paper studies transmission line differential protection with reduced channel requirements from the aspects of data format, sampling synchronization, synchronous monitoring and network security. It puts forward a line differential protection method based on 5G and an optical fiber integrated channel. The focus is on a synchronization method based on the improvement of the reliability of the data channel and on the external synchronization clock, and the real-time synchronization monitoring strategy of multi-mode data to realize the synchronization. Through the simulation test, the method realizes routable differential data processing, reduces the requirements of differential protection for the channel, monitors the sampling synchronization status in real time, improves the reliability of differential protection, and is conducive to the popularization and application of dual channel and three route. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. SGHD0000DKJS2000106).