This paper proposes a simple model for studying ferroelectricity by introducing a screened dipole-dipole interaction Hamiltonan. By minimizing the total energy, the body-centered tetragonal lattice structure is shown to be stable under the screened di pole-dipole interaction, while the cubic structure is not. The effectiveness of this model is estimated by simplifying the model to the nearest-neighbor Ising model for evaluating the physical quantities. The results are in qualitative agreement with experimental data. A method is also suggested to verify the results. In addition, the critical temperature of the 3 D-Ising model for body-centered tetragonal crystals is obtained using the Monte Carlo method.