As an example of severe polluted lake zone in Lake Taihu, the organochlorine pesticide and polycyclic aromatic hydrycarbons (PAHs) in sediment in Wuli Lake was analyzed to determine the accumulation regulation in sediment and potential ecological risk to aquatic system and slurry stockyard after dredging.The results showed that the PAHs in sediment in Wuli Lake were exponentially distributed along the depth and the contents in upper layer were remarkably higher than in the lower layer, but no obvious ecological impact was found.The sediment in Wuli Lake was polluted by organochlorine pesticide in some what degree, especially for hexachloro cyclohexane (HCH) and DDE, but they were possibly safe to aquatic system.The PAHs in soil in slurry stockyard was only one sixth of the PAHs in sediment in Wuli Lake.Eight months after the stockyard was used, the 16 priority PAHs in sediment in the stockyard was still comparable to the original lake sediment, but the contents of PAHs in the aquatic plant (alligator alternanthera) remarkably changed to six times of the original contents before the use of stockyard and the contents of four species of the PAHs were exceeded the ERL but lower than the ERM.The Benzol al anthracene and Chrysene was also detected in the plant stem which was not detected before the use of stockyard.This showed the sediment in the stockyard from the lake dredging would put some threaten on the ecological safety of water plant in the stockyard.