In this paper, we theoretically investigated stress-induced magnetic anisotropy and presented a model based on a unidirectional tensile stress experiment. Firstly, the theoretical model was simulated based on the work of Jiles. Secondly, experiments were conducted, and data under unidirectional tensile stress were collected and analyzed. Finally, the model was developed by correlating the experimental data and theoretical model. Our model provides a good description of stress-induced magnetic anisotropy under unidirectional tensile stresses and lays down a foundation for the quantitative testing and evaluation of stress of ferromagnetic materials through the magnetic method.