In order to expand the applications of giant magnetostrictive materials in the field of precision positioning,an extreme value model of free energy was established with deflection angle of magnetic domain as the independent variable from the microscopic aspect.The model was based on Stoner-Wohlfarth(S-W) model wherein Tb_(0.3)Dy_(0.7)Fe_2 alloy was taken as a research object,and the deflection law of magnetization angle of single magnetic domain was studied through drawing the equipotential curves and changing curves of free energy function under different applied stresses and in different magnetic fields.Research results showed that there were three kinds of magnetization angles of single magnetic domain as for Tb_(0.3)Dy_(0.7)Fe_2 alloy,namely 35.26o,90o and 144.74o; under the action of applied stresses,the magnetization angles θ were deflected to the direction of 90o for the magnetic domains of 35.26o and 144.74o and the magnetization angles ψ were changed and transited to the direction of ψ=135o for the magnetic domain of 90o; the magnetic domain was deflected under the action of small magnetic field for magnetic domain of 35.26o; with the increase of magnetic field intensity,the magnetic domain of 90o had a transition trend to a stationary planar of ψ=ψ0; the magnetic domain of 144.74o had a transition trend to the direction of magnetic domain of 35.26o.These results laid a foundation for the magnetostrictive mechanism and establishment of precision positioning theories of the giant magnetostrictive materials. In order to expand the applications of giant magnetostrictive materials in the field of precision positioning, an extreme value model of free energy was established with deflection angle of magnetic domain as the independent variable from the microscopic aspect. The model was based on Stoner-Wohlfarth ( SW) model selected Tb_ (0.3) Dy_ (0.7) Fe_2 alloy was taken as a research object, and the deflection law of magnetization angle of single magnetic domain was studied through drawing the equipotential curves and changing curves of free energy function under different load and in different magnetic fields. Research results showed that there were three kinds of magnetization angles of single magnetic domain as for Tb_ (0.3) Dy_ (0.7) Fe_2 alloy, namely 35.26o, 90o and 144.74o; under the action of applied stresses, the magnetization angles θ were deflected to the direction 90o for the magnetic domains of 35.26o and 144.74o and the magnetization angles ψ were changed and transited to the dir ection of ψ = 135o for the magnetic domain of 90o; the magnetic domain was deflected under the action of small magnetic field for magnetic domain of 35.26o; with the increase of magnetic field intensity, the magnetic domain of 90o had a transition trend to a The stationary domain of ψ = ψ0; the magnetic domain of 144.74 had had a transition trend to the direction of the magnetic domain of 35.26 o. The results laid a foundation for the magnetostrictive mechanism and establishment of precision positioning theories of the giant magnetostrictive materials.