CoO/g-C3N4 hybrid catalyst is facilely prepared to be application for photocatalytic H2 evolution from water splitting by the vacuum rotation-evaporation and in situ thermal method. The physic and chemical properties of CoO/g-C3N4 are determined by a series of characterization methods. The g-C3N4 with 0.6wt% Co loading exhibits the superior photocatalytic hydrogen evolution activity with H2 evolution amount of 23.25 mmol g-1 after 5h. The obtained 0.6 wt% CoO/g-C3N4 can split water to generate 0.39 mmol g-1 H2 without sacrificial agent and noble metal, while the pure g-C3N4 is inactive under the same reaction condition. The remarkably enhancement of photocatalytic H2 evolution activity of CoO/g-C3N4 composites is mainly ascribed to the effective separation of electron-hole pairs and charge transfer. The work extends new chance for design of low-cost g-C3N4 based photocatalysts with high photocatalytic H2 evolution activity from overall water splitting.