Photocatalytic hydrogen evolution reaction (PC-HER) provides a solution to energy crisis and environmental pollution. Herein, different graphitic carbon nitride (g-C3N4)-based van der Waals (vdW) type II homojunctions have been fabricated and g-C3N4/K-doped g-C3N4 nanosheets have an outstanding PC-HER rate of 1,243 µmol-h−1·g−1 under visible light, higher than that of bulk g-C3N4, doped g-C3N4 nanosheets, and mixed nanosheets. The enhanced PC-HER performance can be ascribed to the cooperative effects of the shortened bandgap, enlarged specific surface area, matched type II energy band structure, “face to face” vdW charge interaction, and peculiarly partite positions of the conduction and valence bands in different layers. Besides, the type II junctions were found superior to binary type II junction. This study highlights the synergistic effect of different strategies in improving the PC-HER capacities of g-C3N4, especially the application of particular vdW junctions, and provides new insights to the structures and mechanism.