The Tangtang granite occurs in the western margin of the Yangtze platform and mainly consists of plagioclase granite. In order to reveal the significance of its petrogenesis, the authors studied the SHRIMP U-Pb dating of zircon and geochemistry of the granite. Geochemical and petrologic data show that the Tangtang granite is characterized by high silicon (SiO₂=72.70%～77.95%), high alkali (ALK=5.68%～7.32%) and peraluminous nature (ASI=1.41～1.78), the average of K₂O/Na₂O ratios is 1.18, and the content of CaO and MgO is very low. Thus, the granite is a typical high-K calc-alkaline S-type granite. It has low REE concentrations and obvious difference between LREE and HREE (LREE/HREE=2.71～4.09), and its trace elements are different from those of the crust. SHRIMP U-Pb dating of the magmatic zircon yielded the age of 1 063.2±6.9 Ma, which should be regarded as the formation age of the granite, and hence the granite was probably related to the Grenville orogenic event. Based on these geochemical characteristics, this paper deals with the petrogenesis of Tangtang granite. It is suggested that the granite was formed by partial melting of argillaceous rocks in the crust. The pattern of bimodel magmatic rocks and the Al₂O₃-SiO₂ diagram both indicate that the formation of Tangtang granite was closely related to the rift environment. The result is consistent with the tectonic setting of 1.0 Ga in the western margin of the Yangtze platform and also corresponds to the Rodinia supercontinent convergence.