Abstract: Abstract: Chlorinated hydrocarbon pollution of groundwater environment has become a worldwide environmental pollution problem. 1,1,1 trichloroethane (TCA) in groundwater is susceptible to a variety of natural degradation mechanisms. Natural attenuation at a 1,1,1 trichloroethane (TCA) contaminated site was investigated using reactive transport model to characterize its potential effectiveness. The results of the sampling and detection indicated that the majority of the contaminant mass was present at 2—6 m in depth, the contaminated area was about 1 000 m2, and natural attenuation processes were occurring at the site. The MODFLOW groundwater model indicated that groundwater was stable and its hydraulic slope was low, which, along with the adsorption factor, slowed contaminant diffusion. Using the adsorption isothermal experiment and the column experiments of the simulation of natural attenuation of TCA in the aquifer, the kinetic parameter of adsorption was 0.06 m3/kg and the kinetic constant for biotic dehydrochlorination of TCA was 0.005 d-1. The contaminated area was predicted to be diminished gradually, and the maximum concentration of TCA to fall below the standard of 300 μg/L in about 5 years. The simulation is of great significance for the groundwater pollution mechanism and the controlling technique of pollutants.