Cyanobacterial blooms is a common phenomenon in large shallow eutrophic lakes such as Lake Taihu, China. When it occurs, a dense algal mass may accumulate in the littoral zone under the action of wind and waves. This algal layer at the surface water can last for a few days and may pose negative influences on local aquatic plants, especially submerged macrophytes. However, there is a severe lack of studies to evaluate the impacts by the algal bloom formation. A great deal of studies showed that some benthic snails can promote the growth of submerged aquatic plants by their grazing activities in clear water lake ecosystems, but in turbid lakes with high concentrations of cyanobacteria, whether the snails still have positive impacts on the growth of submerged plants remains unclear. Here, we conduct a mecocosm experiment with a 15-day duration to explore the influence of cyanobacterial accumulation and snail grazing on the growth and reproduction of submerged aquatic plants. In this experiment, snail Bellamya aeruginosa, submerged macrophyte Vallisneria natans and cyanobacteria were selected from Meiliang Bay of Lake Taihu, China. Our experiment design included four treatments(control, snails only, cyanobacteria only and snails & cyanobacteria). Results showed that high concentrations of cyanobacteria (Chl-a>220 μg/L)strongly inhibited the growth of V. natans. Compared to the control group, the relative growth rate of V. natans in cyanobacteria only group decreased by 40.9%. Meanwhile, the relative growth rate of plants in cyanobacteria & snails treatment group was also 36.4% lower than those in snails only group. Moreover, high concentrations of cyanobacteria suppressed the reproduction of V. natans. The number of Vallisneria ramets in the cyanobacteria only and cyanobacteria & snails group were 56.4% and 64.1% lower than that in the control and snails only groups, respectively. The poor growth and reproduction in treatments with high cyanobacterial concentrations are likely attributed to the shading effect of cyanobacterial blooms on submerged aquatic plants. However, the grazing activities of B.aeruginosa could promote the growth and reproduction of macrophytes in treatments with or without the presence of algal layer. In this experiment, the relative growth rate and number of ramets in snails only and snails & cyanobacteria treatments were evidently higher than those in the control and the cyanobacteria only treatments, respectively. This might be due to the removal of periphyton which adhered to the surface of aquatic plants by the grazing activities of snails B.aeruginosa. Two-Way Analysis of Variance showed that the interactive effects of two factors (cyanobacterial accumulation & snail grazing)in this experiment were no significant and the influence of cyanobacterial accumulation on the growth of V. natans was greater than that of snail grazing. This study suggested that in large shallow eutrophic lakes, the accumulation of cyanobacteria in the downwind littoral zones could seriously suppress the growth of the submerged aquatic plants in several days, but the grazing activities of snails can, to some extent, reduce the impacts by the cyanobacterial blooms and enhance survival ability of plants in the cyanobacteria impacted environments.