National Time Service Center (NTSC) of the Chinese Academy of Sciences (CAS), formerly known as Shaanxi Astronomical Observatory, is the only professional research institute of China which specializes in fundamental research and application study of time and frequency. Established in 1966, NTSC undertakes the task to generate, maintain and transmit the national standard of time (Beijing Time), and operates BPL and BPM Time Service Systems which is among the first batch of major national science and technology infrastructures. Meanwhile, NTSC has built the only experiment platform for space-ground integrated satellite navigation and time service in China, making important contribution to the construction and development of national time and frequency system and navigation satellite system.

NTSC has its base in Lintong, Xi'an, research units in Xi'an National Aerospace Industry Base and Pucheng, Weinan, and time service stations, time service monitoring stations, orbit determination stations all over the country. It is carrying out research on quantum frequency standard, time-keeping, time-keeping theory and method, high-precision time transfer and precise orbit determination, measurement and control of time-frequency, time-user system and equipment, navigation and communication etc.

NTSC has the largest atomic clock group in China and ranks third in the world. It is responsible for determining and maintaining China's coordinating universal time standard (UTC(NTSC))and Atomic time standard (TA(NTSC), and represents China in international atomic time cooperation. The deviation between the national standard time generated and maintained by NTSC and the coordinated universal time standard (UTC) is within 3ns. The stability of time and frequency and its contribution to the calculation of international atomic time are among the top three in the world.

In 1970, the Short-Wave Time Service Station (BPM) was established and started to provide standard time and frequency signal service with the approval of Premier Zhou Enlai. In 1970s, Long-Wave Time Service Station (BPL) was set to meet the needs of the national technology development. BPL began to broadcast after passing the national-level technology test organized by the State Science and Technology Commission in 1986. Since then, China’s timing accuracy has been raised from millisecond to microsecond, driving the time service technology of China into a world’s leading position. This achievement won the first prize of National Scientific and Technological Progress in 1988. In the past five decades, NTSC has built multiple kinds of time service system, such as BPM, BPL, low frequency time-code, telephone, website and communication satellite, providing reliable and high-precision time service for communication, electric power, transportation, surveying and mapping, aerospace, national defense and other industries and departments. At the same time, GNSS Common View, two-way satellite, GNSS PPP and other means are used to provide point-to-point ultra-high precision time and frequency services for important users, which basically satisfies the needs of national economic development, national defense construction and national security.

NTSC has long been engaged in the research and development of various types of atomic frequency standards, including timekeeping atomic clocks, satellite-borne atomic clocks, cesium atomic fountain clocks, and strontium atomic optical clocks. These efforts have provided a fundamental support for the generation and real-time autonomous calibration of national standard time, also offered rich technical reserves for the establishment of time references in various scenarios including space and ground. NTSC researchers innovatively developed high-performance precision frequency measurement equipment.

In the field of satellite navigation, NTSC has creatively developed Chinese Area Position System (CAPS), which met the urgent needs of the country. The realized satellite navigation system time, signal and orbit performance testing and evaluation system, as well as the experiment platform for space-ground integrated satellite navigation time service, have made significant contributions to the construction of China's satellite navigation system.

In the new era, NTSC is brave to take on heavy responsibilities, and undertakes the major tasks of national major scientific and technological infrastructure, such as the construction of high-precision ground based time service system, national time and frequency system. As an important force in the construction of the national space-time system, NTSC will based on national needs, focus on the cutting-edge of the time and frequency discipline, and continue to conduct in-depth and systematic research on time-frequency and navigation technology innovations. It will build NTSC into a research and development base for China's time and frequency standards, time service systems, and satellite navigation. This will provide strong technological support for China's key scientific and technological infrastructure, important strategic equipment, and the sustained development of the national economy, and enable China's time and frequency research and time service capabilities to rank among the world's top.