Heavy metals sequential extraction was applied to examine the spatial occurrence characteristics of Cu，Zn，Pb，Cd，Ni，Cr in sediments of rivers or lakes in Nanjing. The results showed the bioavailability of 6 heavy metals ranked as follow: Cd>Pb>Zn>Cu>Ni>Cr. Cd and Pb exist mainly in reducible state and acid soluble state, and they not only produce secondary pollution on the overlaying water but also have higher risk to aquatic organisms. Moreover, the more human production and living activities affect the water environments，the higher degree of pollution appears, and the migration and transformation of specification of heavy metals become more easily, which should be paid more attention.