Compositive changes in climatic factors, e.g., carbon dioxide (CO2) and precipitation frequency and intensity, affect the strength of species interactions via responses in plants. Therefore, understanding the effects of climate change on plant-herbivore interactions is important to maintain biodiversity as about 70% of insects are herbivorous. However, the interactive effects of CO2 and precipitation on plants and consequences for herbivores are poorly understood. Here, we examined how elevated CO2 and increased watering frequency affect the growth and resistance responses of Aristolochia contorta and the growth performance of its specialist herbivore, Sericinus montela. Elevated CO2 suppressed growth with decreased photosynthesis ability, and increased resistance in plants. In contrast, increased watering frequency partly ameliorated the negative effects of high CO2. Growth performance of specialist herbivores decreased under elevated CO2 condition as a consequence of increased resistance in plants. Due to the significant effects of CO2, we suggest that both the quantity and the quality of host plants as a food would decline, and the growth performance of its specialist herbivore might be threatened as climate change progresses.