Soil salinization limits the growth of agricultural crops in the world, requiring the use of methods to increase the tolerance of agricultural crops to salinity-alkali stress. Arbuscular mycorrhizal fungi (AMF) enhance plant stress adaptation through symbiosis and offer a promising strategy for remediation. However, in non-model crops such as oat ( L.), research has mainly focused on physiological assessments, while the key genes and metabolic pathways involved in AMF-mediated growth and saline-alkali tolerance remain unclear. In this study, we employed integrated multi-omics and physiological analyses to explore the regulatory mechanisms of AMF in oats under normal and saline-alkali stress. The results indicated that AMF symbiosis significantly promoted oat growth and physiological performance under both normal and saline-alkali stress conditions. Compared to the non-inoculated group under normal conditions, AMF increased plant height and biomass by 8.5% and 15.3%, respectively. Under saline-alkali stress, AMF enhanced SPAD value and relative water content by 16.7% and 7.3%, reduced MDA content by 35.8%, increased soluble protein by 21.8%, and decreased proline by 13.3%. In addition, antioxidant enzyme activities (SOD, POD, and CAT) were elevated by 18.4%, 18.2%, and 14.8%, respectively. Transcriptomic analysis revealed that AMF colonization under saline-alkali stress induced about twice as many differentially expressed genes (DEGs) as under non-saline-alkali stressed conditions. These DEGs were primarily associated with Environmental Information Processing, Genetic Information Processing, and Metabolic Processes. According to metabolomic analysis, a total of 573 metabolites were identified across treatments, mainly comprising lipids (29.3%), organic compounds (36.8%), and secondary metabolites (21.5%). Integrated multi-omics analysis indicated that AMF optimized energy utilization and antioxidant defense by enhancing phenylpropanoid biosynthesis and amino acid metabolism pathways. This study provides new insights into how AMF may enhance oat growth and tolerance to saline-alkali stress.