Abstract: Ammonia, as the core raw material of the nitrogen fertilizer industry and a highly potential carbon-free energy carrier, its efficient and low-carbon synthesis is of great significance for ensuring food security and energy transition. Although the traditional Haber-Bosch process is mature and efficient, it relies on fossil energy, has extremely high energy consumption, and requires operation under harsh conditions of high temperature and high pressure （400～500 ℃, 10～25 MPa）, accompanied by a large amount of carbon emissions. Under the background of the “dual carbon” target, it is imperative to develop green ammonia synthesis technologies that can couple with renewable energy and operate under mild conditions. The chemical looping ammonia synthesis （Chemical Looping Ammonia Synthesis） technology decouples the overall reaction into two independent steps of “nitrogen fixation” and “hydrogenation”, ingeniously avoiding the competition adsorption of nitrogen and hydrogen in the traditional process and the thermodynamic equilibrium limitations, providing a revolutionary path for green ammonia synthesis under normal pressure and moderate temperature. The system focuses on the latest research progress of the hydrogen-based chemical looping ammonia synthesis （H₂-CLAS） technology. It elaborates on the basic principles and classification of chemical looping ammonia synthesis technology, compares the advantages and disadvantages of the two technical routes of H₂O-CLAS and H₂-CLAS in detail, and centers on the core of H₂-CLAS technology - the nitrogen carrier. The system reviews the two main types of nitrogen carriers: alkali/alkaline earth metal hydrides-ammonia-nitrogenous compounds （such as LiH/Li₂NH, BaH₂/BaNH）, and transition metal nitride systems （such as Mn₄N, Mo₂N, Co₃Mo₃N）. It summarizes the four optimization strategies: metal doping: introducing transition metals such as Fe, Ni, Co can effectively regulate the strength of metal-nitrogen bonds, reduce the formation energy of nitrogen vacancies, and significantly improve the reaction kinetics and ammonia yield; constructing composite nitrogen carriers: combining transition metals with alkali earth metals or designing dual/multi-metal nitrides to utilize the synergistic effect of multiple components to optimize the electronic structure and open up new mild reaction pathways; carrier modification: using porous carriers such as Al₂O₃, ZSM-5 to disperse active components, enhancing structural stability and nitrogen adsorption capacity; external field enhancement: integrating microwave, plasma, light, and electricity as external field energy to further reduce reaction temperature and energy consumption, and improve energy efficiency by selective heating, generating high-activity species, and changing reaction pathways. The future key directions that H₂-CLAS technology needs to overcome to achieve industrialization are envisioned. In summary, the chemical ammonia synthesis technology, as a distributed ammonia synthesis solution that can flexibly match with renewable energy electricity, represents an important future development direction for green ammonia synthesis. Through interdisciplinary material innovation, mechanism exploration, and engineering scaling, this technology is expected to break through the thermodynamic and energy consumption bottlenecks of traditional ammonia synthesis and provide key technical support for deep decarbonization in the agricultural and energy sectors.