  In this paper, we calculate mass and probability fractions of meson-meson
components of $X(3872)$ in an unquenched quark model. Different from most of
other unquenched quark models, the quark pairs creation operator from $^3P_0$
is modified by considering effects of the created quark pair energy and
separation between the created quark pair and the valence quark-pair. In the
calculation, all the wavefunctions of mesons and the relative motion between
two mesons are obtained by solving the corresponding Schr\"{o}dinger equation
with the help of gaussian expansion method. The multi-channel coupling of
quark-antiquark state with possible meson-meson states are performed. The
results show that the $X(3872)$ can be described as a mixing state of dominant
charmonium state (70\%) and meson-meson components (30\%).
