The microbial counts, type, as well as relationship between microbial counts and the temperature of water in reticulating water system of heating pipeline in Taiyuan were studied, which the main biofouling harmful microbes included slimeforming heterotrophic bacteria, sulfate reducing bacteria, iron bacteria and fungi, respectively. The results showed that the harmful microbes in water system were lower than that of control guideline during heating period, whereas the microbes were higher than that of control guideline, which would result in biofouling of water tube during non-heating period.