Abstract: We applied quantum mechanics/classical mechanics simulations to study excess-electron attachment and ionization of uridine monophosphate anion (dUMP^-) in explicit aqueous solutions. We calculated vertical electron affinities (VEAs), adiabatic electron affinities (AEAs), vertical detachment energies (VDEs), vertical ionization energies (VIEs), and adiabatic ionization energies (AIEs) of the 40 structures obtained from molecular dynamic trajectory. The excess-electron and hole distributions were analyzed in electron attachment and ionization of aqueous dUMP^-. The converged mean VEA (-0.31 eV) and AEA (2.13 eV) suggest that excess-electron can easily attach to dUMP^-. The mean vertical (-0.50 e) and adiabatic (-0.62 e) excess-electron on uracil reveal that main excess-electrons are localized on nucleobases at the most snapshots. The distributions at several special snapshots demonstrate the excess-electron delocalization over nucleobases/ribose or ribose/phosphate group after the structural relaxations of dUMP^2- dianion. The VDE value (2.78 eV) indicates that dUMP^2- dianion could be very stable. Moreover, the mean VIE is 8.13 eV which is in agreement with the previous calculation using solvation model. The hole distributions on uracil suggest that the nucleobases are easily ionized after the irradiation of high-energy rays. In vertical ionizations, the holes would be delocalized over uracil and ribose at several snapshots. Observing the adiabatic hole distributions, it can be found that electrons on phosphate group and holes on nucleobases can be transferred to ribose at the special snapshots in the structural relaxation of neutral species.