Bayan Obo deposit as the second largest niobium ore body in the world, its niobium resources have not been exploited due to its characteristics of “poor, heterogeneous, fine and scattered”. In this paper, based on the geological study of the ore deposit, field emission scanning electron microscope and electron probe microanalysis (EPMA) were used to carry out mineralogical scale analysis of the aeschynite- group minerals in the ore body, in order to determine the co- associated characteristics and element occurrence state, and then explore their utilization properties. The aeschynite- group minerals are AB2X6 type rare earth- rich and radioactive titanium—niobium—tantalate rock minerals. The results show that the aeschynite- group minerals are mainly associated with aegirine, riebeckite, dolomite, magnetite, fluorocarbonate rare- earth minerals, and some sulfide minerals. Most of them are cross- congenial in solid- solution series, with particle sizes ranging from 0.2~2 mm, and the distribution of assemblages can be seen in the hand specimens. The chemical composition is characterized by the enrichment of Nb, Ti and REE elements, in addition to some Ca and Th elements. With the ratio of the atomic numbers of Nb and Ti at the B position combined with the atomic numbers of Ce, Nd and Y rare earths at the A position, the aeschynite- group minerals were classified into nine categories of cerium—titanium- aeschynite, neodymium—titanium- aeschynite, yttrium—titanium- aeschynite, cerium- aeschynite, neodymium- aeschynite, yttrium- aeschynite, cerium- nioboaeschynite, neodymium- nioboaeschynite and yttrium- nioboaeschynite in the Bayan Obo deposit, and mainly dominated by neodymium aeschynite and cerium aeschynite, followed by yttrium aeschynite and neodymium—titanium aeschynite, and the content of Nd- enriched aeschynite with Th was significantly higher. Elemental correlation analysis indicates that there may be two coupled homogeneous substitutions of 2Nb5++Ca2+2Ti4++Th4+ and Nb5++Ca2+Nd3+(Pr3+)+Ti4+. In addition, microscopic observation combined with backscattering images (BSE) reveals that the primary aeschynite was altered by hydrothermal fluids to form Th- rich parisite- (Ce), parisite- (Nd), and a Fe- rich unknown niobium mineral. During the process the REE and Th elements of aeschynite were activated, migrated and enriched, suggesting that there may also be a kind of isomorphous substitution mode for Nb5++REE3++Th4+2Fe2++Ti4++Si4+. Since the aeschynite- group minerals are more enriched in the radioactive element Th than other niobium minerals, they may not be the optimal niobium beneficiation target for the mine in the current production process, and more suitable target minerals need to be selected in the next step.