Abstract: Six kinds of heavy metals in the surface sediment and surface water in the Yihe River were monitored in order to study the effects of the Xiaobudong Rubber Dam on distribution and accumulation of heavy metals in the surface sediment.Samples from eight sites were collected during the dry,wet,and normal seasons.The results showed that the average contents of As,Cd,Cr,Cu,Hg and Pb in the surface sediment were 6.65,0.40,71.21,42.48,0.15 and 41.54 mg/kg,respectively,which were 2.85×103-3.04×105 times higher than those in surface water meeting Grade Ⅲ of China’s national Environmental Quality Standard for Surface Water(GB 3838-2002).Furthermore,the contents of the heavy metals in the sediment increased down the reservoir from the dam,which indicated the acceleration of heavy metal enrichment by the dam.Assessment of the ecological risk of the metals in the surface sediment suggested that As presented low risk,while Cd,Cr,Cu,Hg and Pb presented moderate risk during the water-filling stage.The average risk levels of the metals in the surface sediment were ranked in the order of Cr> Cu> Pb > Hg > Cd > As.It could be concluded that the dam is a contaminant trap where heavy metals accumulate gradually as a result of hydrodynamic changes.