The carbon loaded KNb₃O₈ nanosheets composite has been synthesized for the first time by hydrothermal method, displaying an outstanding performance in photocatalytic H₂ evolution. The optimal C/KNb₃O₈ sample exhibits a H₂-generation rate of 1148 μmol g⁻¹ h⁻¹ under simulated solar illumination, which is 1.8 times that of pristine KNb₃O₈. Various characterizations including N₂ adsorption, XRD, XPS, Raman, DRS, transient photocurrent, EIS, LSV have been applied to investigate the behind mechanism. It is found that the introduction of carbon shows a slight effect on the specific surface area, but obviously improves the optical property and charge separation efficiency. The introduced carbon mainly acts as electron trapper to accept the photoexcited electrons from the conduction band of KNb₃O₈, and hence enhances the efficiency in separating electron-hole pairs, which plays a key role in improving the photocatalytic reaction. The cycling test further demonstrates that the C/KNb₃O₈ has high photocatalytic stability, indicating its good potential for practical photocatalytic H₂ evolution.