Tests to determine internal stress in composites are important, but the internal stress is hard to be detected. Due to the lattice symmetry of Eu3+, Eu3+ can be used as a structural probe. In this work, Eu3+ were doped into the Al2O3-Y3Al5O12 short fibers, which were abbreviated as (Al2O3-YAG: Eu3+)sf hereafter. The (Al2O3-YAG: Eu3+)sf were compounded with 2024 aluminum alloy powder to obtain (Al2O3-YAG: Eu3+)sf reinforced aluminum matrix composites. The structure and luminescence characteristics of (Al2O3-YAG: Eu3+)sf reinforced aluminum matrix composites under continuous tensile stress were characterized by in situ x-ray diffraction and the dynamic spectral response platform. The internal stress of composites was calculated using the Williamson-Hall method theoretically. The (Al2O3-YAG: Eu3+)sf reinforced aluminum matrix composites exhibited red emission and demonstrated luminescence sensing toward the internal stress by the barycenter wavelength of the emission spectrum. The result shows the barycenter wavelength of 5D0 → 7F1 transition of Eu3+ had a regular red-shift with the increase in tensile stress, and the internal stress could be characterized by the shift of barycenter wavelength. The garnered results provide an idea for the development of stress sensor materials based on Eu3+ barycenter wavelength technology.