Aspergillus aculeatus has been shown to stimulate plant growth, but its role in plants abiotic stress tolerance and the underlying mechanisms are not fully documented. In this study, we investigated the mechanisms of A.aculeatus-mediated drought, heat and salt stress tolerance in tall fescue. The results showed that A.aculeatus inoculation improved drought and heat stress tolerance in tall fescue as observed from its effect on turf quality (TQ) and leaf relative water content (LWC). In the same stress conditions, A.aculeatus alleviated reactive oxygen species (ROS) induced burst and cell damage, as indicated by lower H₂O₂, electrolyte leakage (EL) and malondialdehyde (MDA) levels. Additionally, the A.aculeatus inoculated plants exhibited higher photosynthetic efficiency than uninoculated plants under drought, heat and salt stress conditions. The fungus reduced the uptake of Na⁺, and inoculated plants showed lower Na⁺/K⁺, Na⁺/Ca²⁺ and Na⁺/Mg²⁺ ratios compared to uninoculated ones under salt stress. Furthermore, comparative metabolomic analysis showed that A.aculeatus exclusively increased amino acid (such as proline and glycine) and sugar (such as glucose, fructose, sorbose, and talose) accumulation under drought and heat stress. However, there were no differences between inoculated and uninoculated plants except for changes in H₂O₂ level, Na⁺ in the root and photosynthetic efficiency under salt stress. Taken together, this study provides the first evidence of the protective roles of A.aculeatus in the tall fescue response to abiotic stresses, partially via protection of photosynthesis and modulation of metabolic homeostasis.