The Bayan Obo REE-Nb-Fe Deposit is the largest REE deposit in the world. The ore is embedded in all the dolomitic carbonatites and some vein carbonatites. A comparative study on more than 20 areas of igneous carbonatites in the world suggests that the Bayan Obo region is identical to the others in geology. Petrographi-cally there is here an assemblage of carbonatite + ultrabasic+alkaline basic (including lava)+alkaline + REE ore +iron ore; and mineralogically an assemblage mainly of calcite and dolomite with alkali amphibole, felspar, ae-girite, apatite, fluorite, magnetite and REE minerals. The whole-rock composition, trace elements, REE and Sr, Nb, Pb, C and O isotopes show that the rocks have a relationship and a common source. The rocks occur as sheet, pipe and vein with strong liquation and flow structure. There are buried domes, pipes and intersecting faults. A synthetic analysis of the above features indicates that there are, in the Bayan Obo region, remains of Neoproterozoic damaged volcanic edifices, the host dolomitic carbonatites are igneous intrusions along the bed-ding , the Main and East ore bodies are controlled by two volcanic necks, and the Sumt Deposit to the southwest of the host dolomitic carbonatite is controlled by buried pipes.