Oasis ecosystems in Asia's inland arid regions are highly sensitive to climate change and therefore critical for studying prehistoric human-environment interaction evolution. This study reconstructs oasis environmental evolution from similar to 6800 to 3000 cal yr BP using phytolith analysis and ecosystem change rate assessments for the BJH profile in the central Tianshan Mountains. Integrating these results with the summed probability distribution of archaeological C-14 dates, we examine the potential impact of extreme cold events on the decline of the Bronze Age Xiaohe culture. The results reveal a pronounced extreme cooling event between 3461 and 3261 cal yr BP in the study area. This event is evidenced by a sharp decline in the phytolith Iw index, degradation of reed communities, and rapid colonization by wetland herbs, accompanied by falling lake levels and peat development. Mechanistically, this cooling was driven by reduced solar activity and a negative phase of the North Atlantic Oscillation, which induced rapid regional cooling via westerly wind teleconnections. This extreme cooling event likely curtailed mountain runoff through a "temperature-glacier-runoff" feedback, precipitating the collapse of the oasis ecosystem in the terminal reaches of the Kongque River watershed. In contrast, the upper reaches and piedmont zones maintained relatively stable hydrological conditions. The close temporal coincidence of this environmental perturbation with population decline and cultural collapse in the Xiaohe culture's core area suggests that water resource crises in terminal oases were a critical environmental trigger for the reorganization of prehistoric cultural patterns.