The formation energy of vacancy is calculated from, the surface tension of solid. It is found that the theoretical values of vacancy formation energy of metals agree with its experimental values, the vacancy formation energies of metals are directly proportional to its energies of self-diffusion and melting points, and the ratio of the energy of vacancy formation to the energy of self-diffusion, determined by one of the above proportional relations, is 0.43. Besides that, the vacancy formation energy is also a periodic function of atomic number.