In this article, we propose a method to calculate the density of deep traps formed in interaction zones based on a mesoscopic structure and a double-electric layer of polymer nanocomposites. A space-charge modulated breakdown model is then utilized to investigate the electrical breakdown property and its relation to deep traps in interaction zones. The deep traps that formed around the independent interaction zones suppressed the spacecharge accumulation and the distortion of the electric field, leading to the improvement of the dc breakdown strength.