Beryllium (Be), as a critical element, is an essential industrial raw material inaerospace, aviation and the new energy industry. China is a major beryllium consumer with high external dependence. The Baishawo Be- Li- Nb- Ta deposit in northeastern Hunan Province is a newly discovered large pegmatite- type rare- metal deposit; however, the occurrence and ore- forming mechanism of beryllium within this deposit remain poorly understood. Here, we combined geology, SEM, EPMA, LA- ICP- MS and TIMA analysis, to investigate the petrographic and mineralogical features of beryl, tourmaline, quartz, albite, and muscovite of 3# pegmatite in the Baishawo Be- Li- Nb- Ta deposit. The results show that Be is hosted in beryl as an independent mineral phase, but occurs in tourmaline, quartz, albite, and mica in an isomorphic form. Beryl mainly develops in the wall and intermediate zones of 3# pegmatite. The wall zone beryl is light green in color with 2×3×5 cm in size and coexists with albite, muscovite, and garnet. The beryl crystal from the intermediate zone has large grain size (~50 cm), and presents a short columnar, with longitudinal lines parallel to the c- axis on the crystal surface. The beryl from the wall zone has BeO, Li2O, and Cs2O content of 12. 87%~14. 01%, 0. 14%~0. 33%, and 0. 05%~0. 12%, respectively. The BeO content in beryl from the intermediate zone is 13. 38%~13. 96%, and the contents of Li2O and Cs2O are slightly higher than those in the wall zone, which are 0. 25%~0. 39% and 0. 13%~0. 39%, respectively. Quartz has the lowest Be content (0. 20×10-6~7. 13×10-6, average 2. 50×10-6), but muscovite have highest Be content (16. 9×10-6~53. 8×10-6, average 21. 77×10-6) compared to tourmaline (4. 13×10-6~8. 73×10-6, average 5. 94×10-6) and albite (1. 22×10-6~6. 98×10-6, average 4. 54×10-6). It is considered that the 3# pegmatite is of granitic melt crystallization differentiation origin for wall zone pegmatite, but the pegmatite in the intermediate zone is in the magmatic- hydrothermal transition stage, which is subject to the metasomatism of late hydrothermal fluid. In Baishawo Be- Li- Nb- Ta deposit, beryl coexists with alkaline feldspars such as albite, and the BeO contents is up to 13. 44%, which has a significant industrial value and can be used for green selection and smelting by acid flotation. This study provides a reference for the occurrence and genesis of beryllium in rare metal pegmatite deposits, and also a scientific basis for the exploration, development, evaluation, and prediction of beryllium resources in rare metal pegmatite deposits.