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A model pipeline which dynamically simulates the drinking water distribution system was designed and kept running for twelve months with the tap water from Harbin. Biofilm was taken from its inner surface to isolate and identify the bacteria. Some biofilm was also taken from a real pipeline in Harbin. The results of microbiological analysis showed that there were similar dominant species both in the model and real pipeline, implying that those dominant species could grow well and form the biofilm easily under the same water quality and the same operating situation. The species vary with the length of the test period and reach a balance stage after a long test period. Some biofilm was analyzed by a scanning electron microscope for the further study of the bacterial growth. The SEM results confirmed that most of the bacterial growth on the inner surface of the pipeline were cocci and bacilli. In addition, the polymerase chain reaction (PCR) and agarose gel eletrophoresis were used to detect Pseudomonas aeruginosa. Biofilm samples from the model pipeline and the real distribution pipeline were analyzed by PCR. The PCR result showed that there was no Pseudomonas aeruginosa in both of the pipelines. [ABSTRACT FROM AUTHOR]