Agropyron species are recognized as pivotal components of arid grasslands because they supply drought-resistant forage and support ecosystem recovery. To systematically evaluate the drought resistance of this genus, this study examined 13 populations of Agropyron species (three populations of Agropyron cristatum, six populations of Agropyron cristatum var. pectinatum, and four populations of Agropyron mongolicum) under three soil moisture gradients (80%, 50%, and 30% of field capacity) at the seedling stage. A multi-dimensional assessment framework was constructed by integrating morphological and physiological traits using a membership function model and grey relational analysis. The results indicated that drought stress significantly increased root length by 21.54%, leaf water content by 12.99%, and proline accumulation by 31.56%. Agropyron species mitigate desertification through key drought survival strategies, including stomatal regulation, osmoprotectant accumulation, and enhanced antioxidant activity. Based on the membership function scores, the species drought tolerance was ranked as A. cristatum > A. mongolicum > A. cristatum var. pectinatum. These findings establish quantitative criteria for selecting drought-resistant germplasm and reveal the phenotypic plasticity strategies in Triticeae. Moreover, they indicate that A. cristatum represents a key scientific resource for ecological stabilization and desertification control in the arid regions of Xinjiang.