Abstract: PCB biodegradation in constructed wetland could be described quantitatively with a mathematical model,which was established considering the sorption/desorption,sequestration,diffusion and biodegradation processes.The rmdel simulations were performed in this paper to predict the PCBs' degradation behavior,the necessary treatment time and the end point.Using the Monte-Carlo simulation techniques,the contamination risk analysis for PCB biodegradation in constructed wetland was conducted.It is noteworthy that,after 8 years' biodegradation,no less than 69.4% 4-Cl-PCBs in soil would have been degraded wrath 75% probability and no greater than 10.9% 4-Cl-PCBs in soil would continue to contaminate bulk water wrath 75% probability.The necessary treatment time for 4-Cl-PCBs to reach the end point in soil is no greater than 16.20 years wrath 75% probability,and the sequestration part in soil is no greater than 20.9% with 75% poobaility.