Microscopic and macroscopic magnetic responses are widely used for non-destructive testing and evaluating stress. The basic principle is that the magnetic domain pattern and magnetic domain dynamics are highly dependent on applied tensile stress. Understanding the evolution of magnetic domains under the action of multi-field coupling is critical for developing novel magnetic non-destructive testing technology. In this work, the influences of stress on magnetic domain and magneto-acoustic emission signals in polycrystalline materials are investigated based on the magneto-optical Kerr imaging and magneto-acoustic emission detection system. On a macroscopic scale, the mapping relationship between the magneto-acoustic emission signal and stress is established. Microscopically, the influences of the stress and grain boundaries on the magnetic domain patterns are investigated. And a mapping relationship between percentage of supplementary domains and stress is built. Finally, the interrelation between the domain wall dynamics and the magneto-acoustic emission signal is revealed from the nucleation of supplementary domains and their stress-dependent evolution. The results indicate that the magnetoelastic effect reduces the density of supplementary domains and 90° domains, which weakens the magneto-acoustic emission signal. The stress-magneto-acoustic model and the influence of the stress on the magnetic domain in this work reveal the mechanism of magneto-acoustic emission technique for stress measurement. It also provides a theoretical foundation for developing stress-magnetic-acoustic models and magnetic non-destructive testing technology.