In this study benzidine was used to investigate the sorption behavior of aromatic amines in the aqueous-sediment systems. Benzidine may sorb to the sediment matrix after entering aqueous-sediment ecosystems and undergo at least three different fate processes, including cation exchange, hydrophobic partitioning, and covalent binding.  Depending on the ionic strength, the ion composition, pH, and organic carbon content of the system, the three sorption processes may make different contributions to the overall sorption of benzidine in the aqueous-sediment systems. A sorption mechanism based model is presented to fit benzidine sorption behavior at different pH values ranging from 3.1 to 6.9. This model is comprised of three components mathematically: [i] the linear hydrophobic partitioning, [ii] Langmuir-type covalent binding, and [iii] quadratic cation exchange. Nonlinear regression with Sigmaplot indicated that the proposed model fits the experimental data very well. The results suggested that hydrophobic partitioning and covalent binding contributed more to the overall sorption of benzidine than the cation exchange process when solution pH was increased from 3.1 to near neutral. The fitted model parameter of OC-normalized distribution coefficient K_OC (1911-4125 L/kg) was in accordance with the literature value of 2884 L/kg. The covalent binding sites were found to be approximately between 27 and 63 mmol/kg OC under different pH conditions investigated. This model strategy may provide an alternative way to predict the complex sorption processes of aromatic amines in the aqueous-sediment environment.