Two effective flavobacterium strains FCN1 and FCN2 were isolated from the sludge which had been contaminated by coke-plant waste water for a long time.Before isolation,the naphthalene was used to cultivate such sludge for seven weeks as the sole carbon source and its concentration adding to the cultivating system was increased up to 50mg/L gradually.The polycyclic aromatic hydrocarbon degrading characteristics of our isolates themselves and with inorganic ions was studied respectively.The testing results show that our two isolates can transform and degrade anthracene,phenanthrene and pyrene.After 10 hours reaction,the removing rates of anthracene,phenanthrene and pyrene by FCN1 were 84%,69%,80% and by FCN2 were 76%,40%,71% respectively.After 106 hours,the removing rates of TOC caused by anthracene,phenanthrene and pyrene were 70%,54%,69% by FCN1 and 63%,50%,46% by FCN2.The Fe 3+ and Mg 2+ can accelerate the degrading reaction of FCN1.