[Objective] This study was aimed to investigate the degradation characteristics and fermentation optimization of a PCBs-degrading strain. [Methods] The capability of Sinorhizobium melilon on PCBs degradation was studied with different concentrations of 2,4,4′-TCB and 3,3′,4,4′-TCB as the sole carbon source separately. The optimum PCBs-degrading conditions were researched by orthogonal experiment and co-metabolism experiment. [Results] The degradation rate of Sinorhizobium melilon to 2,4,4′-TCB was decreased gradually with the concentration increase of 2,4,4′-TCB. The degradation rates for 2,4,4′-TCB were 93.3% of 1.0 mg/L and 65.1% with the highest concentration up to 50.0 mg/L for 7 days, respectively. The degradation rates were 56.2% of 1.0 mg/L and 22.8% with the highest concentration of 25.0 mg/L for 3,3′,4,4′-TCB, individually. The orthogonal experiment showed that the optimal conditions for degradation process were as follows: pH 7.0, temperature 30 °C, inoculation volume 4.5 mL, medium cubage 25 mL/250 mL. Under these conditions, the degradation rate of the strain was increased from 54.8% to 83.6%. In addition, the degradation rate of PCBs was increased with limonene, corvone and mannitol as co-metabolism substratesby Sinorhizobium melilon. [Conclusion] Sinorhizobium melilon is effective in degrading PCBs and our results have significant application on the study of microbial degradation and environment bioremediation of PCBs.