  We study the fine splitting in charmonium spectrum in quark model with the
channel coupling effect, including $DD$, $DD^*$, $D^*D^*$ and $D_sD_s$,
$D_sD_s^*$, $D_s^*D_s^*$ channels. The interaction for channel coupling is
constructed from the current-current Lagrangian related to the color
confinement and the one-gluon exchange potentials. By adopting the massive
gluon propagator from the lattice calculation in the nonperturbative region,
the coupling interaction is further simplified to the four-fermion interaction.
The numerical calculation still prefers the assignment $1^{++}$ of X(3872).
