The atrazine degrading-bacteria biological activated carbon column，soil-extract biological activated carbon column and the control（CK）column were designed to treat the micro-polluted water by atrazine at low concentration.The removal efficiency of atrazine was investigated and the microbial population dynamics was also analyzed by using the Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis（PCR-DGGE）technique.The results showed that the removal efficiency of atrazine in CK column fell to 30%—40％ while the degrading-bacteria column kept the efficiency around 65%—75% over 140 days operation.The pattern of DGGE showed that the atrazine-degrading bacteria isolated in the lab was relatively dominant after inoculation to the column during the operation which extended the life of the activated carbon.The microbial diversity in the soil-extract column decreased when operating in the oligotrophic condition and the microorganisms from tap water could grow on the three columns during operation.