Bayan Obo deposit is a large Fe- REE polymetallic deposit with large thorium resources. However, iron and rare earth resources are the main minerals developed and utilized at present, while thorium resources are almost used up. For the development and utilization of thorium resources in the future, it is important to find the occurrence state and distribution law of thorium resources in ore deposits and reveal the enrichment process and mechanism of thorium resources. In this paper, based on the results of systematic sampling, analysis and testing in recent years, detailed mineralogical observation and whole- rock chemical analysis were carried out on 570 samples from Baiyunebozhu, East and west mining areas. Independent thorium minerals, mainly silicorite, were identified in different types of ores. Silicorite, except a small amount of which were coated by rare earth minerals, is usually interspersed in rare earth minerals in the form of veins. It shows the characteristics of lag enrichment. The average grade of ThO2 in the mining area is 0.0322%, which is more than 30 times higher than the Clark value of the crust (9.6×10-6). There are obvious differences in ThO2 content among various ore types, and high ThO2 content is distributed in mica, amphibole, girine and fluorite ores. The low content of ThO2 in dolomite ore indicates that thorium mineralization is mainly formed in alkaline hydrothermal metasomatism and fluorination. In addition, thorium mineralization is enhanced with the increase of depth, which indicates that the deposit has good thorium ore- forming potential.