Maize (Zea mays L.) is the most widely cultivated crop worldwide. Drought, intensified by global warming and increasingly frequent extreme weather events, has emerged as a major limiting factor for global maize production. Identifying drought-tolerant germplasm is therefore critical for genetic improvement of stress tolerance. In this study, 138 maize inbred lines representing seven mainstream heterotic groups were subjected to severe osmotic stress using 20% PEG-6000 at the seedling stage. Six morphological traits—fresh weight, dry weight, root fresh weight, root dry weight, plant height, and root length—were measured as indicators of drought response. A multidimensional evaluation framework integrating subordinate function analysis, correlation analysis, principal component analysis (PCA), and systematic cluster analysis was employed to assess drought resistance comprehensively and to compare differential responses among genetic groups.Drought stress significantly reduced all measured traits. Based on the comprehensive drought-resistance D-value, the 138 inbred lines were clustered into fours subgroup: extremely drought-tolerant group, drought-tolerant groups, drought-sensitive group, and extremely drought-sensitive materials group. Fourteen extremely drought-tolerant lines were identified, of which seven belonged to the Reid heterotic group. Cluster analysis further revealed pronounced inter-group differentiation in drought tolerance, with the Reid group showing the highest proportion of highly tolerant genotypes. This advantage is likely attributable to their compact plant architecture, well-developed root systems, and efficient water-use capacity. Collectively, our findings systematically characterize the genetic diversity in drought resistance across major heterotic groups and highlight divergent adaptive strategies under osmotic stress. The elite germplasms identified here provide valuable resources for drought-resistance gene discovery, parental line development, and marker-assisted breeding. Moreover, these results offer a theoretical framework for the targeted utilization and genetic enhancement of drought-tolerant maize germplasm in future breeding programs.