The Beidou satellite navigation system is one of the sixteen major projects identified in the national medium-and long-term science and technology development plan and is an important space infrastructure in my country. Atomic clocks are the core of navigation satellites and directly determine the navigation and positioning accuracy of the system. The on-board hydrogen atomic clock, inter-satellite link and new signal system are together called three key technologies for the new generation of Beidou navigation satellites. The Shanghai Astronomical Observatory of China Academy of Sciences has a good research foundation in time and frequency disciplines. It has been responsible for the timing of world time in my country since the 1960s. In the 1970s, it developed my country's first ground-based active hydrogen atomic clock. With the support of the Knowledge Innovation Directional Project of China Academy of Sciences and the Beidou Major Special Key Technology Research Project, aiming at the application of Beidou navigation satellites on satellites, the Shanghai Observatory has taken the lead in completing the development of my country's first satellite-borne hydrogen atomic clock after years of principle exploration. On September 30, 2015, the first on-board hydrogen atomic clock was launched into space with the new generation Beidou navigation test satellite. It has been operating continuously in orbit for more than three years and is working well. Technological innovation content: 1. The world's first time-division dual-frequency modulation circuit for hydrogen clocks. It uses the time-division control method of atomic transition signals to achieve closed-loop control of the microwave cavity and the constant temperature crystal oscillator, solving the problem of mutual influence between the microwave cavity detection signal and the atomic transition detection signal., achieving the internationally leading temperature coefficient index of spaceborne atomic clocks, providing a guarantee for hydrogen clocks to achieve excellent long-term frequency stability and drift rate indicators; 2. For the first time, an electrode-type microwave cavity was applied to a hydrogen atomic clock. The TE011 mode oscillation was realized by designing an electrode inductive capacitance structure, which effectively improved the Q value of the hydrogen clock microwave cavity and the intensity of atomic transition signals, laying the foundation for the realization of high stability indicators of the hydrogen clock.; 3. A new ionization source system based on domestic power tubes and boron nitride materials was proposed and realized. By using the wave-transparent and heat-dissipating characteristics of boron nitride materials, the problem of reliability reduction of the ionization source due to high heating was solved, and the hydrogen clock ionization source system was ensured. Efficient and reliable operation; 4. Using domestic components and domestic raw materials, the core components of the satellite-borne hydrogen clock such as high-efficiency vacuum adsorption pump, integrated servo control circuit and high-performance magnetic shielding system have been successfully developed, meeting the miniaturization, high reliability and long life of the satellite-borne hydrogen clock. Operation requirements have realized the independent controllability of the core technology and components of the satellite-borne hydrogen clock. Intellectual property rights and application promotion: This project has published 25 papers and authorized 7 patents. From 2015 to 2016, two on-board hydrogen atomic clocks carried out application verification tests on the Beidou Navigation Test Satellite, and verified the importance of on-board hydrogen atomic clocks in improving navigation performance through satellite-ground comparison and on-orbit evaluation tests. value. Among the Beidou-3 global system currently under construction, the Shanghai Observatory has completed the development and delivery of 13 satellite-borne hydrogen atomic clocks, 10 of which have been deployed to all three types of Beidou navigation satellites GEO, IGSO and MEO, and have been launched into space with the satellites. After being turned on, they are all used as master clocks and are operating in good condition. Compared with the on-board rubidium atomic clock of Beidou-2, the long-term prediction accuracy of the on-board hydrogen clock has been improved by more than one order of magnitude, and the prediction error is less than 1 nanosecond (ns) per day, reaching the international advanced level. The on-board hydrogen clock has significantly improved the positioning and timing performance of the Beidou satellite navigation system and made important contributions to the construction of the Beidou satellite navigation system.