In this paper, we report a novel photoanode fabricated by spin-coating n-type CuWO4 nano-ovoids on the surface of fluorine-doped tin oxide (FTO) glass and then modified with p-type Mn3O4 nanospheres using a deposition-annealing method. A novel nanocomposite (CuWO4/Mn3O4) with p/n heterojunction formed on the surface of FTO glass. The characterazation results of the nanocomposite indicate that the two moieties of the nanocomposite intimately contact with each other. The photoelectrochemical tests of the prepared CuWO4/Mn3O4 photoanode reveal that the electrode can produce larger anodic photocurrent and show enhanced incident photon-to-current efficiency (IPCE) than the bare CuWO4 photoanode does. Moreover, the PEC tandem cell assembled by using the CuWO4/Mn3O4 electrode as photoanode and Pt plate as counter electrode demonstrates enhanced photocatalytic activity and stability for photoeletrochemical (PEC) water splitting. The amount of hydrogen and oxygen, collected from the counter chamber and the photoanode chamber, separately, reached to 5.0 mu mol and 2.3 mu mol, respectively, under 2 h simulated sunlight irradiation at 1.20V vs. RHE bias without any sacrificial agent. The remarkable performance of the nanocomposite anode owe to the formed heterojunction structure in the nanocomposite, leading to high photoexcited charge transfer and separation.