  In this work the effects of defects in the superconducting phases of the
twisted bilayer graphene (TBG) are investigated. A will-accepted low energy
effective model and a non-magnetic impurity potential to mimic defects are
employed. Different superconducting pairing symmetries, including $s$-wave,
$(d+id)$-wave and $(p+ip)$-wave pairing, are considered. In single impurity
case, the local density of states (DOS) are calculated for the pairing
symmetries above. For different pairing symmetries the number and property of
bound states induced by defects are different. In multi-impurity case, the
phase diagrams are calculated in terms of effective gap and the strength and
density of impurities. In unconventional superconducting phases, namely
$(p+ip)$-wave and $(d+id)$-wave phases, superconductivity will be destroyed by
impurities with strong strength or concentration. These results can in
principle be detected in scanning tunnelling microscopy (STM) experiments, and
therefore the pairing symmetry, at least whether the superconductivity is
conventional or unconventional, may be determined.
