Graphitic carbon nitride (g-C3N4) has emerged as a promising photocatalyst, but poor charge separation and low surface area limit its activity. Here, we report a hydrothermal method to generate hydrogen bonded supramolecular complex via water-based homogeneous supramolecular assembly, which is a promising precursor to fabricate porous and oxygen-doped g-C3N4. The hydrothermal treatment provides a homogeneous environment for hydrolysis of melamine to produce cyanuric acid and reaction of cyanuric acid with remained melamine to create the in-plane ordering and hydrogen bonded supramolecular complex. The complex can template uniform nanoporous structure and also provide an opportunity for O-doping in the g-C3N4 network upon calcination in air. The resulted g-C3N4(GCN-4) possesses high surface area, well-defined 3D morphology and oxygen-dopant in the lattice. Subsequently, the visible light absorption, charge separation, and wettability are considerably enhanced. This catalyst exhibits higher hydrogen evolution rate by 11.3 times than the bulk g-C3N4 under visible light irradiation, with apparent quantum efficiency of 10.3% at 420 mn.