Abstract: In order to improve the degrading efficiency of polycyclic aromatic hydrocarbons (PAHs) in biochemical treatment system of coal chemical wastewater,a highly efficient phenanthrene degrading strain with phenanthrene as the sole carbon source was isolated from biochemical effluent and identified based on 16SrDNA sequence.By means of examination of the physiological and biochemical characteristics of the degrading bacterium,the optimum growth conditions of the degrading bacterium were determined.Besides,effects of humic acid on strain hydrophobicity and degrading capacity were also investigated.The results showed that the strain was identified as Rhodococcus sp.XY916 and named XY916,with its optimum growth pH of a weak alkaline and tolerable mineralization ranging from 0 to 20 000 mg/L.XY916 could grow well in the solution with phenanthrene content of 120 mg/L.The hydrophobicity of XY916 and the apparent solubility of phenanthrene were improved simultaneously under the effect of low concentration of humic acid,thereby enhancing the contact area between XY916 and phenanthrene,and promoting the degradation of phenanthrene with a removal rate up to 95.3%.