The original burial fossil woods excavation at the bottom of the Chetougou formation in Xiejia section, Xining Basin, is not only the first found of the big plant fossil in the arid-semiarid region in NW China, but also greatly significant to research the evolution of plant ecological environment and even the tectonic movement in northeastern Tibetan Plateau. Through the comprehensive analysis of the buried fossil woods characteristics, rock-layer facies and sedimentary environment, we consider that they are adult trees growing near the bank of river, and spacing in the rows ranging from 3-8 meters, which formed the good plant communities with a certain spatial structure. Then,the uplift of the vicinal mountains and the development of arid climate in this area, the plants were buried and the metasomatism with plaster took place, and then formed the calcium sulfate fossil woods, which could show the climate deteriorated in the region since the early-Miocene.