Holocene pedo- stratigraphic sequence was established for the Erfangcun Ruins to the east side of the Lajia Ruins in the Guanting Basin of Qinghai Province through field investigation and pedological and sedimentological analysis. A reliable chronology framework for soil and sediments was made using SAR and OSL for the samples systematically collecting from key strata. The results indicate that the fertile Heilu soil, which formed on the eolian loess deposit over the Yellow River terrace land during the Holocene climatic optimum, became valuable land resource and facilitated the development of the primitive arable farming in the Guanting Basin. However, global climatic decline from about 4200 a BP caused serious disasters for the region. The multiple earthquakes, in combination with storm rain in related to strong convections along the margin of the Tibetan Plateau, induced enormous flashfloods and mudflows during OSL age 3940~3780 a BP, equivalent to 14 C age 3850~3600 a BP. These disastrous surface processes resulted in an interruption of the Heilu soil formation. The farmland with fertile cultivable Heilu soil was blanketed by rigid clay or sand of about 1. 0~4. 0 m thick. These had not only ruined the large settlement (4150~3850 a BP) of the Qijia Culture which sustained on millet cultivation, but also caused a decline of the soil and land resources over the Yellow River terrace land. These mean that the global climatic deterioration from about 4200 a BP affected the environmentally sensitive region over the northeast margin of the Tibetan Plateau. Disastrous surface processes caused the serious degeneration of soil and land resources along the Yellow River banks. These factors all drove the primitive arable farming of millet cultivation to shift into mixed nomadic and arable farming of the Xindian/Kayue Cultures at 3600 a BP. These results are very important in understanding environment change, natural disasters and evolution of the human- land relations in the northeastern margin of the Tibetan Plateau.