To reveal the petrogenesis of Baitai granite in Jiulong area and its relationship with rare metal mineralization, petrographic, whole- rock geochemistry, LA- ICP- MS zircon U- Pb geochronology, zircon trace element geochemistry and Hf isotope geochemistry were studied in this paper. Samples from the Baitai biotite monzonitic granite are characterized by high SiO2 contents （69.01%~70.55%）, high K2O (3.86%~4.99%), high alkali (K2O+Na2O=7.41%~8.18%), low CaO (1.49%~2.2%), low MgO (0.44%~0.57%), with σ of 2.03 ~ 2.43, and A/CNK of 1.07~1.14. These granite samples could be ascribed to peraluminous—weak high- K calc- alkaline series, with the characterics of enriched in large ionic lithophile elements (K and Rb), and depleted in high field strength elements (Nb, P and Hf). In chondrite normalized rare- earth element pattern, they show obvious right deviation type characterized by enrichment of light rare earth elements and depleted in heavy rare earth elements. The biotite monzonitic granite was formed at 213 ~ 212 Ma, and the zircon εHft) values ranges from -7.4 to -1.1, with the TDM2 age of 1.6 ~ 1.2 Ga. In conclusion, we propose that the Baitai I- type granite developed in a postcollisional extensional regime in the Late Triassic, and that it was related to an induced mantle upwelling after the delamination of thickened lithosphere following the final compression collision of the Songpan—Garze terrane. At the same time, the Baitai pegmatite- type beryllium deposits are closely related to the Baitai granite, which are derived from the residual crystallization products of the Baitai granite.