The magnetization model of a magnetostrictive force sensor was studied based on Fe-Ga alloy. The magnetic path of the sensor was optimized with 3D finite element method. Simulation results showed that the field distribution became linear when the magnetic path was optimized. In order to analyze the influence of biased field and loaded stress on material magnetization, the magnetization model was developed based on the homogeneous energy equation. The magnetic field and stress were taken as the independent variables in the Gibbs free energy formula thus the model could respond to both field and stress. The model was numerically solved using Newtons iteration method. In order to verify the model, a testing system was developed and both Fe-Ga alloy and Terfenol-D were tested. Comparisons of simulations and experiments showed that the proposed model could predict the changing of the magnetization properly. The influence of the biased field could be predicted as well. Comparisons of Fe-Ga alloy and Terfenol-D showed that Fe-Ga was more sensitive to the biased field and the hysteresis nonlinearity was lower than Terfenol-D. Since there is no annealed stress in Terfenol-D, it is observed negative magnetization when the material is subjected to cyclic stress with low biased field.