Through the geometry optimization of the ground state of the magnesium oxide molecular, and the theoretical calculation by using b3p86 method combined with 6-311 + + G basis set, the ground state electronic structure of the Magnesium Oxide molecule under the external electric field (-0.015 ~ 0.015 AUA.U.) was obtained. The effect of external electric field on the bond length, energy, energy level distribution, frequency and dipole moment of Magnesium Oxide molecule was discussed. The results show that the electric field effect has obvious effect on the molecular structure of the MgO, and the study can provide some reference for the further study of the MgO in the fields of industry, medicine, feed and food etc.