The research of the relationships among free-living bacteria, attached bacteria and different algal species can provide valuable evidence for understanding the reason of algal bloom development under nutrient limitations. Significantly positive relationships between chlorophyll a and attached bacteria in Microcystisbloom ponds and between chlorophyll a and free-living bacteria in other algal bloom ponds were observed. Microcosm experiments further confirmed the synchronized growth of Microcystis and attached bacteria as well as Pediastrum and free-living bacteria. Carbon and bacteria stimulation experiments suggested that extracellular organic carbon from Microcystis was more complex, inducing specific attached bacterial communities and markedly high extracellular enzymes, which can strongly fuelled Microcystis development. On the contrary, dissolved organic carbon from Pediastrum was simple and suitable for free-living bacteria, which can made a distinct effect on Pediastrum growth depending on the degree of nutrients uptake by free-living bacteria. Based on the above results, it can be proposed that the reason of Microcystis bloom breakout in Chinese shallow lakes should be attributed to the close nutrient complementary relationship between Microcystis and specific attached bacteria mediated by dissolved organic carbon and extracellular enzymes at the development of bloom, which might provide scientific support for the research of Microcystis bloom control.