Abstract: The sediment in Huangpu River was chosen as the suspended solids and of phenanthrene was a model compound of PAHs in this study. The mechanism for the adsorption phenanthrene on sediments in natural water was found. The results show that the adsorption of phenanthrene on sediments is of multi molecular layers one, which can be well described by BET model. The competitive adsorption is occurrence between methenol and phenanthrene. Film diffusion is the controlling step for adsorption rate in the adsorption process of phenanthrene on sediments. These are all related to the structure and properties of phenanthrene in comparing with other PAHs.