Abstract: White water of the wire pit was sampled from the PM2 in UPM(Changshu) Mill. By the conventional pure culture method, 20 dominant microbial strains were selected. Thereafter, 4 strains of these microorganisms, which were obviously different in shape, color and some other common characteristics, were used to conduct further analyses (N1,N2,N4,N16). The phylogenetic relationship of the 4 strains was determined by sequencing the 16S rDNA. Taxonomy of these strains was also studied through physiological and chemical tests, and morphorlogical observation. The experiments indicated that N1 and N2 were Klebsiella pneumoniae, N2 was Klebsiella pneumoniae Rhinoscleroma, additionally; N4 was Sphingomonas azotifigens; N16 was Enterobacter radicincitans. The thicker capsule of strain N1 and N2 against to strain N4 and N16 implied that N1, N2 were Klebsiella pneumoniae, which likely to be the main disease bacterium that brought about pollution to biofilm of the paper machine.