The composition of blockages in polymer flooding oilfields is complex, and the blockages mechanism is unclear. In view of conventional depolymerization system is not highly targeted, the unblocking effectis uneven. In this paper, the composition and micromorphology of polymer plugging in an oil field in Bohai Sea were analyzed. A kind of synergistic depolymerization system, nanoemulsion CPA-NA is developed. The mechanism of synergistic effect of nanoemulsion is also discussed by molecular dynamics simulation. The results show that the polymer blockage is composed by 22.7% crude oil, 7.7% polymer, 34.3% water, and 25.3% inorganic minerals, of which the content of resins asphaltene in the crude oil accounts for 28.1%. The phenomenon of crude oil binding on the surface of polymer blockages is obvious. The polymers could form micelles, and bind, embed, then adhere to crude oil and inorganic minerals, forming complex polymer blockages, under the action of high valent metal cations. Nanoemulsion CPA-NA is a homogeneous dispersion system with oil core and water shell. It has an ultra-low interfacial tension, which can effectively solubilize heavy components in crude oil and synergistically degrade polymer plugging. Molecular dynamics simulation shows that the mechanism of synergistic depolymerization: nano-emulsion molecules penetrate into the space between asphaltene and resin of heavy oil, destroy the accumulation between asphaltene and resin, peel off heavy oil components, improve liquidity, promote the penetration of depolymerizer into polymer blockers, so as to give full play to depolymerization. CPA-NA nano-emulsion has been applied in Bohai oilfield, and the construction effect is good, which provides a new technology to for depolymerization of polymer flooding oilfield.