Micromagnetic simulation was carried out to investigate the behavior of ferromagnetic materials at a very small length scale, at which the materials usually exhibit different properties compared with those of the corresponding bulk materials. By solving the time and spatial dependent Landau-Lifshitz-Gilbert (LLG) equation in reciprocal space using fast Fourier transformation (FFT) technique, the equilibrium magnetization state was, thus, achieved. The hysteresis loops were also simulated, from which the relation of coercivity and characteristic length was established. Besides, the effect of external stress on coercivity was also taken into consideration. The results showed that at such length scales the external stress strongly affected the magnetic behavior of ferromagnetic materials.