The refinery-activated sludge was cultivated with pyrene as one single source of carbon and energy. The community diversity of pyrene degradating strains was studied by extracting the genomic DNA of microbial community in 6 different periods，amplifying the bacterial 16S rDNA V3 fragment with touch-down PCR method，and separating the products by denaturing gradient gel electrophoresis (DGGE). The result showed that there was an obvious syllogistic process in community structure and amount of dominant populations. The concentration of pyrene was a main factor to influence the community diversity of pyrene degradable strains.