Over decades, the ever-increasing demand for compact, lightweight, low-cost and flexible energy storage devices has spurred the development of high performance dielectric-polymer-based capacitors from industry and academic. Despite previous effort, to date, the capacitive performance such as discharged energy density of dielectric polymers is still greatly limited, posing an obstacle to their wide applications. Herein, in this work, we demonstrated a facile while highly efficient approach to dramatically enhance the capacitive performance of dielectric polymers represented by poly(vinylidene fluoride) (PVDF) through the employment of manganese dioxide (MnO2) particles and their geometric structure modulation. Making use of the semi-conductive nature and unique tunnel structure of MnO2, one can suppress the conduction loss, promote the space charge polarization and interfacial coupling polarization and consequently boost the capacitive activities of composites. Furthermore, through geometric structure optimization of MnO2, the capacitive performance of composites were strengthened to be more impressive, i.e an energy density and a power density of 24.5 J/cm3 (350 MV/m) and 1.98 MW/cm3 (200 MV/m), respectively. The results demonstrated the efficiency of MnO2 with optimized geometric structure in enhancing capacitive performance of dielectric polymers, providing a new paradigm to explore high performance capacitive polymer composites.