To explore the condition of heavy metal pollution of Taihu Lake, the contents and spatial distribution of Cd, Pb, Cu and Zn in surface sediments of Taihu Lake were studied respectively. BCR three stages sequential extraction procedure was applied to investigate the speciation and contents of four heavy metals (Cd, Pb, Cu, Zn) in the surface sediments of Taihu Lake. And the bioavailability of these four heavy metals was also determined preliminarily. At last the contamination and potential ecological risk of these elements were evaluated by potential ecological risk index. The results indicated that all 4 elements in surface sediments of Taihu Lake were enriched to some extent, especially Cd. All of these four metals existed mainly in extractable fractions which included weak soluble fraction, reducible fraction and oxidisable fraction, and the bioavailability of four metals varied with a descending order of Cd > Pb > Zn > Cu. The comprehensive assessment results showed that Cd was the primary element with high ecological risk while Pb, Cu, Zn were slight, and the order of ecological risk was Cd > Pb > Cu > Zn.