Herein, a novel 2D/2D heterostructure, phosphorus‐doped carbon nitride nanosheet/zinc porphyrin metal–organic framework (MOF) (HPCNN/ZnPMOF), is elaborately fabricated through an electrostatic self‐assembly process for photocatalytic H 2 evolution from water splitting. The as‐prepared HPCNN/ZnPMOF 2D/2D photocatalyst displays the highest H 2 evolution rate of 65.3 mmol g −1 h −1 under simulated solar irradiation, which is 2.2 and 49.1 times higher than that of HPCNN and ZnPMOF, respectively. The enhanced photocatalytic activity can be ascribed to the intimate contact interface and the shortened migration distance formed by the unique 2D/2D structure, resulting in dramatically enhanced separation and transfer efficiencies of hole–electron pairs. Furthermore, P doping endows carbon nitride with more separation sites of photoinduced charge carriers and consequently establishes type‐II heterojunction with ZnPMOF. This work shed lights on the potential of designing the highly efficient MOF/g‐C 3N 4 2D/2D system for water splitting H 2 evolution.