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Aquatic plants and associated herbivores are expected to perform better under the rising atmospheric CO2 concentration brought about by climate change. However, it is not clear how increasing CO2 affects herbivory on aquatic macrophytes. In this research, we set four treatments (A group: ambient air without snails; AS group: ambient air with snails; E group: elevated CO2 without snails; and ES group: elevated CO2 with snails) and studied the effects of low (0-0.5mg/L) and high (4-8mg/L) CO2 concentration on the growth, morphology, and chemical traits of the macrophyte Vallisneria spiralis (Angiosperms: Hydrocharitaceae) and the snail Radix auricularia (Pulmonata: Lymnaeidae), and the relationships between them in the laboratory. We found that herbivory decreased the total biomass of V. spiralis by 28.6% and 25.3% under low and high CO2 conditions, respectively. Compared with A group, ES group reduced the total plant biomass by 43.3%. Elevated CO2 and herbivory both affected the growth of V. spiralis and change its resource allocation patterns. Total nitrogen content in V. spiralis leaves decreased under herbivory condition, and total phenols increased under the interactions condition between elevated CO2 and herbivory. However, total C content of R. auricularia increased under elevated CO2 condition. These results could provide valuable insights into how climate change affects plant-herbivore interactions and food web structure in shallow inland waters.