The Yulong porphyry Cu-Mo deposit in eastern Tibet is one of the largest copper deposits in China. The formation of the deposit has been regarded to be related to a monzogranilic composite intrusion in the center of the deposit, but the genetic relationship between mineralization and the composite intrusion remains poorly constrained. Based on field geological mapping and drill hole logging along No. 8 section, the authors identified a suite of granite porphyry stocks from the composite pluton. The stocks include abundant quartz-feldspar A-type veins, and some quartz shows unidirectional solidification texture and pegmatite/aplite texture. These characteristics indicate that the magma was once water-saturated. Additionally, high-grade (>0.6%) copper mineralization is distributed closely around the granite stocks, with high-temperature A-type veins within the stock, and meso-temperature quartz-sulfide D-type veins far away from the stock. Hydrothermal alteration surrounding the deposits is generally characterized by concentric zones from an inner potassic zone outward to phyllic and argillic alteration zones, and an outer propylitic and skarn zone. The potassic alteration zone well overlaps the granite porphyry stocks. Based on above observation, the authors hold that the granite porphyry stocks are ore-forming intrusions at Yulong.