Understanding spatial differences in the millennial-scale environmental evolution on the central-western Tibetan Plateau is essential for revealing mechanisms of climate changes. In this study, a 787-cm sediment core covering the last 18 thousand years (ka) from Ngamring Co was analyzed for pollen to infer long-term vegetation changes. In addition, a modern pollen dataset (n = 964) and fossil pollen records (n = 6) from the western-central Tibetan Plateau were used to investigate past precipitation changes, using the quantitative method Weighted Averaging Partial Least Squares (WA-PLS) and the Cyperaceae/Chenopodiaceae ratio (Cy/C). Pollen spectra from Ngamring Co indicate that arid alpine desert was distributed around the lake from 18 to 14.6 cal ka BP as revealed by low pollen concentration and a high proportion of exogenous arboreal pollen, followed by a shift to alpine steppe until 10.3 cal ka BP. Alpine shrub-steppe (dominated by Cyperaceae, Artemisia, Poaceae, and Hippophae) emerged afterwards and was progressively supplanted by drier alpine steppe with sparse vegetation cover after 3.5 cal ka BP. Quantitative reconstructions and the pollen ratio reveal a distinct transition (characterized by progressive precipitation reduction and amplified aridity) since the Mid-Late Holocene across the central-western Tibetan Plateau, gradually weakening from west to east. This aridification is likely linked to the weakening summer monsoon. In addition, pollen and observational data suggest a recent shift in desertification trends on the centralwestern Tibetan Plateau.