Abstract: The Cenozoic graben structures known as the Dongco graben, oriented nearly N-S and more than 80 km long, are well developed in the Tuonamu region, Qiangtang basin, Xizang, and consist of fault uplift zone and fault depression basin. These graben structures have an important effect on the local geomorphological features and drainage framework. The tectonic activities in the graben were initiated during the Miocene, and are still active in modern times.The formation of above-mentioned tectonic activities may be constrained by the deep-seated thermod ynamic mechanisms. The oil and gas anomalies are observed along the normal faults in the graben, indicating that the active faults in the graben may play a significant destructive role in the preservation of oil and gas pools.