Up to now, rational design and facile synthesis of photocatalysts with high activity and low cost remain a great challenge. Here, noble-metal-free graphene and NiS co-modified g-C3N4 composite photocatalyst was prepared using an one-step hydrothermal method. The ternary composite displayed enhanced photocatalytic water splitting activity. When the weight ratios of RGO and NiS were 0.25% and 3%, respectively, the highest H-2 evolution rate was achieved, which was 21.8-fold that of bulk g-C3N4. The introduction of NiS and RGO dual cocatalysts promoted the separation of photogenerated electron-hole pairs and improved the light absorption of g-C3N4, thus enhancing the photocatalytic activity. This work provides significant guidance for the modification of photocatalytic materials with noble-metal-free cocatalysts to realize high-efficient photocatalytic water splitting for hydrogen generation.