Abstract：Time synchronization technology is widely used in industrial automation, precision measurement and control, and military command information system. The IEEE 1588 precision time protocol provides sub-microsecond network time synchronization to meet the high precision measurement and control needs of the industry. White Rabbit（WR） time synchronization is a distributed time synchronization solution based on synchronous ethernet, IEEE 1588v2 protocol and all Digital Dual Mixer Time Difference（DDMTD）, which provides sub-nanosecond synchronization accuracy. The SAE AS6802 protocol is a high-precision, fault-tolerant, development-ready clock synchronization protocol that provides Time-Triggered Ethernet（TTE） with a globally synchronized clock of the required accuracy and a wide range of distributed determinism. This article reviews the research and development of these three time synchronization technologies, analyzes the advantages and disadvantages of the three technologies, and looks forward to the future development trend of network time synchronization technology.