Water shortages and water pollution are current issues in ecosystems around the world, and the stress induced by drought can further increase negative impacts on agriculture in these areas. In the present experiment, we examined the effect of mild drought on wheat plants grown in association with the wheat aphid Sitobion avenae Fabricius (Hemiptera: Aphididae) in 2019 and 2020. Using plot experiments, we tested the hypothesis that mild drought tends to enhance the performance of this wheat aphid by changing the nutritional quality of the wheat plants. We found that mild drought treatment significantly increased aphid abundance and population growth rates. Also, mild drought significantly increased total amino acid concentration of the wheat ear as well as concentrations of key amino acids, including Arg, Ile, Leu, Lys, Phe, Try, Gly, Ala, Tyr, and Cys in 2019, and Arg, Ile, Leu, Lys, Gly, and Cys in 2020. Mild drought led to a shift in the composition of amino acids in the plants, causing cascading effects at higher trophic levels. Such changes suggest that the carrying capacity of the environment with respect to aphids will increase if mild drought events continues to increase in frequency with climate change.