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 Pekar 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 space-time evolution of the electron density. It is shown that the electron density increases with the temperature when the temperature is lower，and the electron density decreases with the temperature when the temperature is higher. At the same time，we found that sometimes the electron density vibrates with the temperature，and its change is slowed down with the strength of coupling increasing.