Abstract: A sediment core Esdr1 from Shudu lake was analyzed for grain size and magnetism. Accurate sediment chronology was established by ¹³⁷Cs. By comparing the grain-size and magnetism proxies to document and precipitation data, we discussed the influence of disafforestation and dam on depositional environment. Both magnetic susceptibility and grain-size proxies increase remarkably at 17~14 cm(1958-1970) depth. Precipitation data reveal a decrease during this period. But county annals record that there was intense disafforestation from 1958 to 1963. Vegetation cover deterioration will lead to serious erosion in drainage area. More sand and silt transport to lake,which causes grain-size and magnetic susceptibility values to increase. Both precipitation and constructing dam affect lake sediment composition. The precipitation increased from 1988 to 2002. A dam was constructed at the lake outlet in 1988,which enlarged lake area. Finer sediments deposited with streamflow disappearance. Although precipitation slightly increased from 1988 to 2002,it is obvious that dam construction has more influence on lake sediment environment. It may be why grain size in Esdr1 core became finer at 8~0 cm depth (1988-2002).