Grazing damage has been recognized as one of the most important factors determining species distribution and community structure in aquatic plants. The effects of snail hervivory on interspecific relationship between two aquatic macrophytes, Elodea nuttallii and Vallisneria spiralis were investigated using a 2×2 factorial experiment design. Results showed that Elodea has a competitive advantage over Vallisneria at various densities. When the macrophyte density was low, plant competition and snail herbivory had not significantly affected the growth of Vallisneria. At a high density, grazing activity of snail stimulated the growth of Vallisneria, and plant competition suppressed the plant growth. Intensive plant competition and grazing damage suppressed the growth of Elodea at various densities. The regulation mechanisms of snail grazing activity on interspecific relationship between the two macrophytes were discussed.