The interaction mechanism of benzo［a］pyrene（BaP）-cadmium（Cd）combined pollution in water body with Arthrobacter oxydans was investigated by using HPLC and FTIR analytical techniques. The experimental results showed that BaP，Cd and BaP-Cd combined pollution all posed adverse effects on the normal growth of the strain with the sequence of influence BaP-Cd＞Cd＞BaP. The concentrations of BaP and Cd in aqueous media were reduced to 0.39 mg·L-1 and 0.65 mg·L-1，respectively，from the initial concentration of 1 mg·L-1 after treatment for 5 days at 30℃，130 r·min-1.Adding H2O2 at a specific concentration and keeping the treatment system under alkaline condition were favorable to disposing of BaP-Cd combined pollution. Infrared scanning analysis showed that the structure of BaP changed with the action of microbe. Hydroxy，carbon-carbon double bond，aminoacyl and alkyl were confirmed to be the key functional groups for the strain to biodegrade BaP and adsorb Cd.