  The single impurity effect on the graphene-based superconductor is studied
theoretically. Four different pairing symmetries are discussed. Sharp resonance
peaks are found near the impurity site for the $d+id$-wave pairing symmetry and
the $p+ip$-wave pairing symmetry when the chemical potential is large. As the
chemical potential decreases, the in-gap states are robust for the $d+id$
pairing symmetry while they disappear for the $p+ip$ pairing symmetry. Such
in-gap peaks are absent for the fully gapped extended $s$-wave pairing symmetry
and the nodal $f$-wave pairing symmetry. The existence of the in-gap resonance
peaks can be explained well based on the sign-reversal of the superconducting
gap along different Fermi pockets and by analyzing the denominator of the
$T$-matrix. All of the features can be accessed by the experiments, which
provide a useful probe for the pairing symmetry of graphene-based
superconductors.
