To understand laser-assisted field evaporation of semiconductors and insulators at the microscopic level, we study the time evolution of the electronic and atomic structure of a MgO cluster in high electrostatic fields subjected to strong laser pulses. We find that the critical laser intensity for evaporation decreases linearly as the electrostatic field strength increases. The optical absorption enhancement in high electrostatic field is confirmed by the redshift of the optical absorption spectra, the reduction of the energy gap, and the increase of the absorption cross section.