  Thermal conductivity of graphene nanoribbons (GNR) with length 106~{\AA} and
width 4.92~{\AA} after isotopic doping is investigated by molecular dynamics
with quantum correction. Two interesting phenomena are found: (1) isotopic
doping reduces thermal conductivity effectively in low doping region, and the
reduction slows down in high doping region; (2) thermal conductivity increases
with increasing temperature in both pure and doped GNR; but the increasing
behavior is much more slowly in the doped GNR than that in pure ones. Further
studies reveal that the physics of these two phenomena is related to the
localized phonon modes, whose number increases quickly (slowly) with increasing
isotopic doping in low (high) isotopic doping region.
