The electronic structure of the quantum-dot molecules in an electric field is investigated by the finite element method with the effective mass approximation. The numerical calculation results show that the valence bond of the quantum-dot molecule alteates between covalent bonds and ionic bonds as the electric field increases. The valence-bond property can be reflected by the oscillator strength of the intraband transition. The bound state with the highest energy level in the quantum-dot molecule gradually changes into a quasibound state when the electric field increases.