In this work, the energy gaps (E g ) of highest occupied orbitals and lowest unoccupied orbitals, trap energies (E t (e) and E t (h)) and excited energies of polyethylene model compound, typical defect compound, acetophonene, and 33 designed additives are obtained using density functional method at B3LYP/6-3111G(d, p) level. The correlation between trapping-electrons (holes) abilities of additives and molecular frontier orbitals is established, and a new understanding for trap mechanism based on chemical molecular orbital levels is given for the first time which could be used to filter qualitative additives as volt-age stabilizers of polyethylene. The role of trap energies and the energy gaps on discussing space charge accumulation and electric breakdown is analyzed in detail. A molecular design strategy for potential additives of cross-linked polyethylene insulated high-voltage cable is shown based on conjugation effect, substituents character, and polycyclic aromatic compounds.