Abstract: Based on the analysis of the historical data of the uranium mill-tailing site in southern China,the actual conditions are generalized,and a coupled reaction-transport numerical model is set up to simulate the representative radionuclide-uranium (Ⅵ)adopting the PHREEQC-Ⅱ code. This work is carried out with the various parameters such as dispersion coefficient,the diffuse coefficient,pH,the mixratio,and the retardation coefficient. The sensitivities for the parameters are also analyzed in this paper. The results of this simulation accord with the actual information observed on site1 So the simulation,which can be a reference for analogical research,can provide theoretical base for environment assessment and treatment after the decommis-sion of uranium mill-tailing sites.