Niobium is a rare metal and strategic resource that plays an important role in modern industry. The Bayan Obo Nb-REE-Fe deposit is a super-large niobium deposit with 2.2 Mt Nb₂O₅ resources at an average grade of 0.13%. Therefore, it is very important to find out the occurrence and distribution characteristics of niobium. The niobium mineral in the Bayan Obo deposit has the features of fine, scattered and thin, which is difficult to find by polarizing microscope, so it is impossible to achieve the research purpose. On the basis of petrography and EDS analysis, the occurrence and distribution characteristics of niobium in deep aegirine-rich Nb-REE-Fe ores in the Bayan Obo main mine were studied by means of AMICS and EPMA. The results show that the average content of Nb₂O₅ in the ores is 0.15%. Niobium mainly occurs in columbite, pyrochlore, aeschynite, baotite and ilmenorutile, the total mineral content of 5 niobium minerals in aegirine-rich ores is 0.40%. The particle size of niobium mineral is fine, < 90 μm accounts for more than 88.16%, and it is a subhedral or anhedral grain. The results of EPMA show that the average content of Nb₂O₅ in columbite, pyrochlore, aeschynite, baotite and ilmenorutile is 73.46%, 63.42%, 28.43%, 16.03% and 15.81%, respectively. Niobium is mainly occurred in the form of independent niobium minerals, and a few occurred with other minerals in the form of isomorphism and inclusion. Niobium minerals are scattered and mainly distributed among aegirine, monazite and apatite or aegirine, barite and bastnäsite particles, often associated with aegirine, fluorite, monazite, bastnäsite, barite, apatite and other minerals. The chemical composition of niobium minerals is considerably complex, and the phenomenon of isomorphic substitution is common. The chemical formula of 5 kinds of niobium minerals is calculated and quite complex. There are obvious correlations between Nb and some elements in niobium minerals, and there are selective substitution of Ca²⁺ and Th⁴⁺ ions in aeschynite, this further indicates that complex isomorphic substitution of niobium minerals occurs during the formation process. Nb₂O₅ has the highest occupancy rate in pyrochlore and the lowest in baotite, the former is nearly 32 times of the latter. The total occupancy rate of 5 niobium minerals was 90.51%. Pyrochlore, columbite, ilmenorutile and aeschynite are the main industrial minerals for extracting niobium. This study provides a basis for the mineral processing of niobium in order to make full use of the niobium resources in Bayan Obo.