A highly crystalline perylene imide polymer (Urea‐PDI) photocatalyst is successfully constructed. The Urea‐PDI presents a wide spectrum response owing to its large conjugated system. The Urea‐PDI performs so far highest oxygen evolution rate (3223.9 µmol g−1 h−1) without cocatalysts under visible light. The performance is over 107.5 times higher than that of the conventional PDI supramolecular photocatalysts. The strong oxidizing ability comes from the deep valence band (+1.52 eV) which is contributed by the covalent‐bonded conjugated molecules. Besides, the high crystallinity and the large molecular dipoles of the Urea‐PDI contribute to a robust built‐in electric field promoting the separation and transportation of photogenerated carriers. Moreover, the Urea‐PDI is very stable and has no performance attenuation after 100 h continuous irradiation. The Urea‐PDI polymer photocatalyst provides with a new platform for the use of photocatalytic water oxidation, which is expected to contribute to clean energy production. A crystalline perylene imide polymer photocatalyst with the highest oxygen evolution performance is achieved. The polymer can be reused over 100 h without any decrease in performance overcoming the poor stability of the organic photocatalysts. The superior photocatalytic performance comes from the suitable energy band and the robust built‐in electric field contributed by the highly crystallinity and large molecular dipole.