It is well known that the interfacial region between the polymeric matrix and nanofiller plays a very important role in tailoring the electrical insulation properties of nanocomposite. In this study two type of polyhedral-oligomeric-silsesquioxane (POSS) are doped into epoxy (EP) to investigate the tailoring of interfacial traps that can limit the mobility of charge carriers and enhance the breakdown strength. Incorporating acryloxypropyl POSS (AP-POSS) to EP matrix improves the breakdown strength than that of pristine EP and octaphenyl POSS (OP-POSS). The molecular simulation and experiments identifies that the compatibility between EP/POSS and trap depth is dependent on the interfacial interaction energy and crosslinking density. The side groups of AP-POSS has large number of localized energy states and higher electron affinity (EA) that can tailor deeper traps and restrain the mobility of electrons in EP/AP-POSS. The interfacial compatibility of POSS side groups with EP tune the interfacial traps and dielectric characteristics.