Aiming at the problems of high residual stress and insufficient plasticity of UNSR30003 cobalt‑based elastic alloy ultra‑thin foils after large‑deformation cold rolling， the 0.1 mm ultra‑thin cold‑rolled foil with an accumulative deformation of 97.4% was taken as the research object. The regulation mechanisms of microstructures， mechanical properties and V‑spring elastic service response of alloy foils were investigated under three aging processes： low‑temperature single‑stage aging （450 ℃）， high‑temperature single‑stage aging （500 ℃）， and high‑low‑temperature two‑stage aging （450 ℃+750 ℃）. The results show that the cold‑rolled alloy exhibits submicron lamellar deformed microstructures， and shear bands penetrating multiple deformed grains are observed within the distorted matrix. The low‑temperature single‑stage aging at 450 ℃ achieves the peak strength （ultimate tensile strength of 2 820 MPa， hardness of 549.23HV） via fine dispersed precipitates and inherited dislocations， whereas the elongation after fracture decreases to 3.3%. The high‑temperature single‑stage aging at 500 ℃ promotes matrix recovery and precipitate coarsening， yielding a preliminary strength‑ductility balance. The two‑stage aging process of 450 ℃×300 min+750 ℃×80 min can effectively balance strength and ductility； an ultimate tensile strength of 1 600 MPa is maintained while the elongation after fracture increases to 6.7%， which is 19.64% and 103.03% higher than those of the cold‑rolled state and the low‑temperature single‑stage aged state， respectively. Moreover， its elastic modulus （205 GPa） and resistance to elastic deformation are superior to those of the cold‑rolled foil. Through hierarchical precipitation and stepwise stress‑release mechanisms， two‑stage aging induces substantial dislocation rearrangement and relieves residual stress， realizing the synergistic optimization of strength， ductility and elastic stiffness of the alloy foil. This work provides a reference for formulating heat‑treatment procedures of ultra‑thin precision elastic alloy components.