By using Bi2O3-doped Ba0.3Sr0.7TiO3 (BSBT) fibers prepared via electrospinning and modified by dopamine as dielectric fillers, BSBT/P(VDF-TrFE) flexible nanocomposites are fabricated by solution casting. A low loading of BSBT nanofibers leads to a large increase in the dielectric constant and breakdown strength. In particular, the discharged energy density of the nanocomposites is significantly enhanced several times in comparison with the pure polymer matrix. The enhanced breakdown strength and discharged energy density could be attributed to the combined effects of the surface modification, large aspect ratio and paraelectric polarization behavior of the BSBT fibers. The present work indicates the enhancing potential of energy density on the polymer-ceramic composite by the paraelectric nanofiber fillers.