Abstract: In this paper, the structure and function of microbial communities in water system of Changde City were analysed asing PFUbio-monitoring method, and three functional parameters were put forward on the basis of MacArthur-Wilson's model. Besides, two structural parameters are determinated as well. Meanwhile, water quality of 16 stations for four seasons from 1986—1987 is analysed, and the chemical combined pollution index（p）is advanced. The results show that biotic parameters(HI, Seq, Gand T_90%) are closely correlated with the chemical combined pollution index（p）. The species diversity indices（d） could also reflect the pollution level to a certain extent. It is demonstrated that PFUbio-monitoring method is really a new rapid, accurate and economic way.

Key words: Microbial community, PFU, Bio-monitoring method, Structural parameter, Functional parameter