Time is an important basic physical quantity and an important technical support for scientific research and nation building. Many big countries in the world have their own national independent standard time and perfect timing system. China's standard time — Beijing time is established and maintained by the National Time Service Center of the Chinese Academy of Sciences. The long-short wave timing system independently developed by the center is a social welfare-oriented big scientific project, which solves the high-precision timing problem urgently needed for economic construction and national security. After continuous upgrading, the system has become an indispensable technological infrastructure for the development of Chinese society. This book details the working principle and timing service of long and short wave timing systems, international cooperation agencies, and the application of high-precision time in various fields of the national economy. It is a popular time science popularization book and also a technical guide for time application.