Arbuscular mycorrhizal fungi (AMF) can form mutually beneficial relations with more than 80% of vascular plants, and the existence of the symbiote is of significance in promoting the growth and stress tolerance of host plants. AMF can obtain the photosynthate carbohydrates from host plants, and in the meantime, effectively promote the nitrogen (N) uptake by host plants via the absorption of various N sources by mycorrhiza mycelia, resulting in the N exchange at population or community level, the improvement of host plants nutrition and metabolism, and the strengthening of the stress tolerance of host plants. However, there are still in debates in which ways the symbiote absorbs and transfers N and what the mechanisms the N metabolism and translocation from AMF to host plants. This paper reviewed the mechanisms of N metabolism and translocation in the symbiote and the effects of carbon and phosphorous on the N metabolism and translocation. The roles of AMF in the N allocation in host plants and the related ecological significance at community and ecosystem levels were briefly elucidated, and some issues to be further studied on the N metabolism in the symbiote were addressed.