A highly crystalline perylene imide supramolecular photocatalyst (PDI‐NH) is synthesized via imidazole solvent method. The catalyst shows a breakthrough oxygen evolution rate (40.6 mmol g−1 h−1) with apparent quantum yield of 10.4% at 400 nm, which is 1353 times higher than the low crystalline PDI‐NH. The highly crystalline structure comes from the ordered self‐assembly process in molten imidazole solvent via π–π stacking and hydrogen bonding. Further, the excellent performance ascribes to the robust built‐in electric field induced by its high crystallinity, which greatly accelerates the charge separation and transfer. What is more, the PDI‐NH is quite stable and can be reused over 50 h without performance attenuation. Briefly, the crystalline PDI‐NH with strong built‐in electric field throws light on photocatalytic oxygen evolution, showing a new perspective for the design of organic photocatalysts. A highly crystalline perylene imide supramolecular photocatalyst (PDI‐NH) is successfully constructed via π–π interaction and hydrogen bonding. The PDI‐NH performs a breakthrough oxygen evolution rate (40.6 mmol g−1 h−1), exceeding most of photocatalysts. The high crystallinity of PDI‐NH ensures the built‐in electric field, acting as a kinetic force to promote the charge separation.