Excitonic effect, originated from the strong Coulomb attraction between electron and hole, plays an important role in the photocatalytic process of polymeric materials but has been long ignored. In view point of hot-carriers generation, the dissociation of Frenkel excitons is proposed as an effective way to improve the photocatalytic performance of polymeric photocatalysts. Herein, by taking graphitic carbon nitride (g-C3N4) as an example, we verify that endowing g-C3N4 with electron storage ability can facilitate exciton dissociation by extracting electrons from bound electron-hole couples around the electron stotage sites, therefore enhancing the hot-carriers harvest and suppressing the charge recombination. Benefiting from these advantages, the as-prepared material demonstrates excellent photocatalytic performance for both H-2 evolution and H2O2 generation. As a result, the apparent quantum yield (AQY) for H-2 evolution at 420 nm reaches 55%, which is much higher than most of the reported polymeric materials. The study described here offers a new way for designing advanced polymeric photocatalysts toward high performance solar energy conversion via excitonic engineering.