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 the long and short wave time service system 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 is responsible for determining and maintaining China’s Atomic time standard（TA(NTSC)）and coordinating universal time standard（UTC(NTSC)）with its time-keeping atomic clock group which ranks top one in China and the forth in the world. With NTSC representing China in the International Atom Time (TAI) 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 conducted the research of quantum frequency standard, maintaining certain strengths and highlights in the development of time-keeping atomic clock and spaceborne atomic clock. The cesium atomic clock developed by NTSC has continuous operation capacity for more than 30 days and has reached a frequency stability of 2E-13τ-1/2... Progress has also been made on Strontium atomic optical clock. We have measured spectroscopy of the intercombination transition of 88Sr and realized a single optical frequency comb mode for laser colling of the strontium atoms. Up to now, the Strontium optical clock is under closed-loop measurement and performance estimation.

In the field of satellite navigation, NTSC has creatively developed Chinese Area Position System(CAPS) by taking advantage of its long-term technical accumulation in the field of time frequency, which met the urgent needs of the country. A test and evaluation system for time, signal and orbit performance of satellite navigation system and an experiment platform for space-ground integrated satellite navigation time service were built. It has made outstanding contributions to the development and 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 aim at the top-notch time and frequency science; actively develop innovative research on time frequency and navigation technology from the perspective of national strategy and security. The goal is to make NTSC a real base for the research and development of national time and frequency standard, time service system and satellite navigation, and drive China’s time service and time frequency research level into world’s leading class. NTSC will truly become the key technical infrastructure, important strategic resources and scientific and technological support for the sustainable development of the national economy.