Abstract: The granite rock body located in Guoganjianianshan area, Qiangtang, Northern Tibetan Plateau mainly includes biotite adamellite and granite aplite dike and intrudes into Late Triassic Wanghuling Formation and Late Carboniferous - Early Permian Zhanjin Group-complex. LA-ICP-MS U-Pb dating were carried on the zircons of this granite rock body and the dating results showed that it was formed in Late Triassic (210.3Ma±2.6Ma). This age is slightly later than the metamorphic peak time of the high-pressure metamorphic belt in this area and the age of the rhyolite in lower Wanghuling Formation. Geochemistry studies indicate that this granites belong to high-potassium peraluminous calc-alkaline granites and were formed in post-collisional tectonic setting and by the magmatic activity of the decompression process after the collision and thickening of lithosphere, which means that the tectonic setting of Guoganjianianshan area was transforming from collision stage to intraplate stage and entered post-collision stage.