The objective of this study was to examine the atrazine biodegradation pathway and its genes of the bacteria Arthrobacter FM326, and to understand the degradation mechanism. Our laboratory has found that Arthrobacter FM326 is a highly efficient atrazine-degrading bacteria. A suspension of FM326 was grown in an inorganic salt medium containing atrazine, and during cultivation the content of atrazine and its degradation products were determined every 24 h to reveal the FM326 atrazine degradation pathway. The results revealed the expression of the degradation genes trzN, atzB and atzC during cultivation and that the atrazine content of the medium was decreased in the presence of FM326 when compared to the control group. During cultivation of FM326, hydroxyl atrazine levels increased at first then stabilized during the training process, before declining at 120 h. The cyanuric acid content increased at first and then decreased, and was significantly reduced in FM326 when compared to the control, while the ammonia nitrogen content increased gradually and was significantly increased when compared to the control. There was no significant change in the pH of the FM326 and control cultures. FM326, which expresses atrazine-degrading genes, could completely degrade atrazine into CO₂ and NH₃ and did not accumulate cyanuric acid in culture.