  In the $e^+e^-$ annihilation processes $e^+e^-\to D^0\bar{D}^0, D^+D^-$ near
or above the threshold of $D\bar{D}$, there are not only the resonance
contribution $e^+e^-\to \psi (3770)\to D^0\bar{D}^0, D^+D^-$, but also the
continuum contribution through virtual photon directly $e^+e^-\to \gamma^*\to
D^0\bar{D}^0, D^+D^-$. The amplitudes through virtual photon directly and
through resonance can interfere seriously. We consider the continuum and
interference effect in the $D\bar{D}$ production process in $e^+e^-$
annihilation. We find that the effect is significant near and above the
threshold of the $D\bar{D}$ mesons.
