Kuramoto et al. calculated the activation energy for dislocation loop migration by integrating the force–distance curve. Their method has a great potential for the determination of migration energy in many cases. However, the validity of the application of their method to point defect migration has not yet been proved, because the migration of point defects is a thermally activated process and the physical meaning of the force in the force–distance curve has not been clarified. In this study, the validity was investigated by three methods to calculate the vacancy migration energy. In the first method, the migration energy was obtained by definition from the difference in potential energy between the equilibrium configuration before migration and the saddle point configuration (Method 1) using a statistic lattice relaxation method. The second method involved a molecular dynamics simulation based on an absolute reaction rate theory (Method 2). The third method involved the integration of the force–distance curve obtained by the statistic lattice relaxation method mentioned above (Method 3). The calculation model used was a two-dimensional hexagonal lattice and the Morse potential for Cu was used. The migration energies obtained by Methods 1, 2 and 3 were 0.391 eV, 0.394±0.009 eV and 0.392 eV, respectively. As these values were similar, the validity of Method 3 was demonstrated.