Drought stress, as a global challenge, severely constrains crop production. However, cerium oxide nanoparticles (CeO?-NPs) offer a new strategy for enhancing crop drought tolerance due to their unique redox properties. In this experiment, plants were treated with 25 mg/L CeO?-NPs, which was determined as the optimal concentration through preliminary trials. Combined with drought stress, systematic measurements of plant growth and physiological parameters were conducted. The results showed that drought stress caused severe negative effects on alfalfa growth and development, while CeO?-NPs treatment significantly alleviated these impacts. Comprehensive comparisons revealed that 25 mg/L CeO?-NPs provided the most substantial mitigation of drought stress and was therefore selected as the optimal concentration for subsequent experiments. Specifically, compared to drought stress alone, foliar application of CeO?-NPs increased alfalfa growth parameters including plant height, leaf area, fresh weight, and relative water content （RWC）by 16.39%, 47.33%, 45.01%, and 65.53%, respectively; Chlorophyll content (SPAD) increased by 14.48%, and maximum photochemical efficiency (Fv/Fm) increased by 21.13%; The relative electrical conductivity and malondialdehyde (MDA) content decreased by 60.61% and 46.62%, respectively; Hydrogen peroxide (H?O?) and superoxide anion radical (O???) content decreased by 50.78% and 48.58%, respectively; The activities of ascorbate peroxidase (APX), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) increased by 30.77%, 24.83%, 44.77%, and 20.00%, respectively; The content of the osmotic regulator proline (Pro) and soluble sugars (SS) increased by 40.78% and 34.16%, respectively. This study indicated that CeO?-NPs can synergistically regulate the growth and physiological metabolism of alfalfa through multiple pathways, including maintaining cell membrane stability, improving photosynthetic performance, alleviating oxidative damage, enhancing antioxidant enzyme activity, and increasing the content of osmotic regulatory substances, thereby enhancing its drought tolerance. It was of great significance for the ecological restoration of degraded grasslands and vegetation reconstruction in arid regions.