The theory of stress-impedance effect in amorphous alloys was established by introducing stress-induced anisotropy and magnetic anisotropy and solving Maxwell's equations and Landau-Lifshitz equation with the Gilbert term. The established theory can be used to explain the stress-impedance effect, and the calculation results were in good agreement with the experimental results. We calculated the stress-impedance change with different anisotropy parameters, and reached important conclusions both in theory and for applications.