Coke plant wastewater was treated by an anaerobic-aerobic (A/O) biofilm system. A lab-scale experiment, during which semi-soft media were packed in both the anaerobic and the aerobic reactors, was carried out. The influence parameters, such as HRT, C/N ratio, OLR, and the recycling flow rate on the performance of the system, were studied. The results showed that a sufficient carbon source was important to the performance of bio-degradation system. The COD removal rate increased from 64.15% to 83.28% by raising C/N in wastewater from 2.5 (no external carbon source) to 5. But the effluent COD concentration was still a little higher than the discharge standard. In order to make it meet the discharge standard, a deep treatment, coagulation, was applied, which was proved as an effective method. Then the effluent COD concentration can be brought to lower than 200 mg·L-1. The NH4-N removal rate in this system was satisfactory, being higher than 99%. In addition, it was almost not affected by both C/N ratio and coagulation treatment. The results show that the system is feasible to treat coke plant wastewater.