On the condition of electric-LO phonon strong coupling in parabolic quantum dot, we obtain the eigenenergy and the eigenfuctions of the ground state and the first excited state by using variational method of Peakar type. This system in quantum dot may be employed as a two-level quantum system-qubit. When the electron is in the superposition state of the ground state and the first excited state, we obtain the time evolution of the electron density. It is shown that the period of oscillation decreases with the strength of coupling increasing when the confined length is constant. And the period of oscillation increases with the confined length increasing when the strength coupling is constant.