There are only 5 wells drilling through sedimentary cover and into the basement in Sichuan Basin, and the study for the forming age and tectonic environment is relatively weak. The core material of the Wei117 illustrates the basement is composed of granitoid in Weiyuan area of Sichuan Basin. The results of Zircon SHRIMP U-Pb dating of basal granites show that the crystallization age is 794±11 Ma, Neoproterozoic, which is consistent with the crystallization age of the granites in basin edges. Combining with the geochemical characteristics and genetic types of magma, the granite was formed in the transformation from compression to stretch environment. It was the product of the transformation stage from plate subduction orogeny to continental intracontinental rifting, and it belonged to the initial breakup stage of Rodinia supercontinent. It is thought by synthetical analysis that 800 Ma is an important geological period in Sichuan Basin. It is the main period of formation of the basement, and important change of the nature of the tectonic movement. Over this period, Sichuan Basin was in stretch environment of the continental rift.