As one of the essential elements for plant, nitrogen (N) plays an important role in predicting the primary productivity in terrestrial ecosystems. On the other hand, arbuscular mycorrhizal fungi (AMF), a group of ubiquitous soil fungi that form symbiotic association with the majority of the terrestrial vascular plants, play a vital role in plant growth by providing their host plants with mineral nutrients such as phosphorus (P) and N, and trace elements. AMF can also protect plants from drought stress, pathogen infections and heavy metal contaminations, and improve soil structure by influencing soil aggregation dynamics. Recent studies on AMF and N cycling were mainly focused on the N forms absorbed by AMF and the N metabolism and translocation in the symbiosis. It has been well demonstrated that AMF can take up different N forms such as inorganic N, amino acids, and even complex organic N. AMF prefer to assimilate ammonium than nitrate in most circumstances. The N transfer and translocation via AMF has also been extensively studied. Various N sources are firstly incorporated into arginine (Arg) through the urea cycle in the extraradical mycelium (ERM), and then transported to the intraradical mycelium (IRM) possibly with polyphosphate (PolyP). Finally, Arg is catabolized through the catabolic arm of the urea cycle in the IRM, releasing NH₃/NH₄⁺ into arbuscules. In contrast to good knowledge of N metabolism in the mycorrhizal symbiosis, the possible involvements of AMF in soil N cycling processes such as mineralization of organic N, N fixation, nitrification, denitrification and leaching has been largely overlooked. However, AMF may mediate the soil N cycling process via different pathways from the smallest to the largest spatio-temporal scale, and much attention has been paid to the involvement of AMF in soil N cycling in recent years. The interaction of AMF and other functional microbial groups responsible for N cycling has been particularly studied. It has been well demonstrated that AMF had remarkable effects on diazotrophic, nitrifying and denitrifying microbial communities in soil microcosms or under field conditions. AMF were also shown to reduce soil inorganic N loss via leaching in microcosm-based studies. Taken together, AMF can serve as an important influencing factor for individual soil N cycling processes. Furthermore, the belowground common mycorrhizal networks could essentially affect N transfer and re-allocation among different plants in ecosystems, and thus have important ecological impacts on aboveground plant community and ecosystem stability. Moreover, all AMF hyphae have a high N content, thus the N pool in AMF mycelia could be similar in magnitude to that in roots considering their ubiquity in terrestrial ecosystems. The fungal hyphae also have a rapid turnover rate, indicating that AMF play an unappreciated role in global N cycling. This paper summarized the recent research progresses in N metabolism in AM symbiosis, including N species assimilated by AMF, and the N metabolism genes in AMF. Simultaneously, the potential role of AMF in mediating the soil N cycling processes and its ecological significances in ecosystems were discussed in details. Some important issues in relation to the involvement of AMF in soil N cycling were also proposed for further research.