Abstract: The formation mechanism and the forming time of the physical weathering layer in western Qaidam basin are determined by study of paleo?climatic evolution and regional tectonic evolution since Paleogene. The physical weathering layer is formed by dual role of the dry and cold extreme plateau climate and the intense tectonic compression and deformation during the late Himalayan movement. The physical weathering layer, water layer and oil layer in this area constitute obvious“triple?section style”in vertical. The water level under the physical weathering layer appears diachronous phenomenon, thus it cannot serve as a marker bed for stratigraphic isochronal correlation. In drilling engineering, the physical weathering layer could be easily resulted in circulation loss and borehole collapse for it to reduce seismic signal?to?noise ratio and impact seismic data acquisition