Abstract: We've adopted sandstone detrital component analysis in Cenozoic strata of Ganchaigou area, western Qaidam basin, to analyze the provenance systematically. The microscopic identification and content statistics results of the sandstone components showed that the major types of sandstone are arkose and lithic arkose, and sedimentary rock debris is main in this area. Some signature minerals and debris are identified from sandstone components. The appearance of these special minerals and debris and its content vertical change on section indicated that the sedimentary provenance changed obviously near the boundary of upper Ganchaigou and lower Youshashan formations, implied a sedimentary transformation event occurred at the transformation era from Oligocene to Miocene, which happened at about 20Ma ago, in western Qaidam basin. This event was also supported by a series of evidence in other areas of northern Qinghai-Tibet Plateau. It is an important clue to study the tectonic uplift history of the northern margin of Qinghai-Tibet Plateau.