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Lake sediment is the recorder of historical climate fluctuation and basin environment change. This study collected the Ximencuo Lake sediment in source area of the Yellow River, analyzed organic matters and geochemical elements of the core, obtained nearly environment changes of the past 1,720 years. The results showed the environment evolution process of the 47-cm columnar core can be divided into four stages: below 32 cm (before 900 A.D.), corresponding to the cool and wet climate; 32-20 cm (900 A.D-1300 A.D.), corresponding to the warming temperature and decreasing precipitation; between 20-3.5 cm (1300-1900 A.D.), the stage is more consistent with the Little Ice Age, and precipitation gradually reduced; 3.5-0 cm (since 1900A.D.), this is the twentieth Century warming period with increasing temperature and reduced precipitation. Phosphorus content increased rapidly in the last 20 years, reflecting the continuously increasing human interventions, bur before this period, the P content w*as low and stable, indicating the natural background of regional phosphorus content. [ABSTRACT FROM AUTHOR]