Establishing local built‐in electric field of 2D semiconductors is one of the promising strategies to regulate the oriented charge delivery to active centers for enhancing photocatalytic performance. Herein, a novel heptamolybdate polyanions‐intercalated porous g‐C3N4 ([Mo7O24]6−‐pCN) catalyst with integrating highly desirable visible‐light photocatalytic features is reported. After intercalation, the apparent reaction rate constants (kapp) of [Mo7O24]6−‐pCN for bisphenol A (BPA) and 4‐chlorophenol (4‐CP) photodegradation are remarkably enhanced, which are 9.0 and 6.4 times faster than those of pCN, respectively. Analogously, the kapp values of [Mo7O24]6–‐CN for BPA and 4‐CP removal are also improved by contrast with CN. The experimental results and density functional theory calculations indicate that a local built‐in electric field is formed in [Mo7O24]6−‐pCN with a polarization direction from aromatic rings of g‐C3N4 to the inserted [Mo7O24]6− clusters. Driven by the electric field, photogenerated carriers can be efficiently separated for better reactive oxidative species (ROSs) production. These O atoms are also proved as adsorption sites for phenols, greatly reducing the migration distance of ROSs and thus improving photocatalytic performances. This work offers a reliable strategy to construct local built‐in electric field via polyoxometalates intercalation for effective solar energy conversion and phenolic wastewater remediation.