Drought is the main meteorological threat to plants and limits plant growth, development, and adaptation to environmental changes. However, root-shoot communication plays a vital role in improving tomato plant drought tolerance, especially when cultivars are grafted onto drought-tolerant rootstock. In this study, the relationship between photosynthetic capacity and reactive oxygen species (ROS) in response to drought stress was studied in tomato grafted with different drought-resistant tomato seedlings. To determine the drought-relieving effect of drought-tolerant rootstocks, we measured the effects of grafting on plant growth, net photosynthetic rate (Pn), ROS accumulation, and antioxidant enzyme activities in tomato leaves and roots under drought stress. Plant growth and Pn were significantly inhibited by drought, but ROS accumulation and antioxidant enzyme activities were significantly increased. Treatment with drought-tolerant tomato seedlings significantly increased plant growth and increased Pn under water-deficit conditions compared with those grafted with drought-susceptible rootstock. In addition, the plants grafted with drought-tolerant seedlings had increased activities of partial antioxidant enzymes, leading to decreased ROS production. Our results indicate that tomato grafted with drought-tolerant seedlings alleviated the phytotoxicity and oxidative damage caused by drought by regulating antioxidant enzymes under drought stress.