Abstract: By combining climate change data and archaeological discoveries，evidence shows that warm and wet conditions during the Holocene Climatic Optimum promoted the development of ancient cultures along the northeastern margin of the Qinghai-Tibetan Plateau. This scenario is manifested in the following categories：（1） human activities greatly increased along with the warming temperatures during the Holocene Climatic Optimum；（2）the mode of microlithic culture activity changed significantly from the late Pleistocene to the early Holocene as the settlement patterns developed from temporary camps into relatively fixed settlements；（3）the improvement of water resources and climate conditions during the warm period stimulated the expansion of Yangshao and Majiayao Cultures in the Eastern Valley. This included the formation of the Eastern Valley Majiayao Culture that coexisted with the Western Plateau Microlithic Cultures between 6 and 4 ka BP. The two coexisting culture systems participated in exchange during which the Weastern Plateau Microlithic Cultures obtained pottery，agriculture，and Neolithic technologies，promoting their entrance into the Neolithic.

Key words: Holocene Climatic Optimum, the northwest margin of the Qinghai-Tibetan Plateau, human activities