Graphitic carbon nitride is considered as one of the most potential photocatalysts for utilizing solar energy. Herein, an efficient route of rapid high-temperature treatment fat 800 degrees C in air for 0-20 min) was developed to modify pristine graphitic carbon nitride. It was found that, after rapid high-temperature treatment, the obtained photocatalysts showed greatly enhanced photocatalytic H-2-evolution activities (around 25.5 times) under visible-light irradiation attributed to the following reasons. More active sites for photocatalytic reaction were provided by the significant increase of surface areas. The generation, separation and transfer of photo-generated carriers were effectively promoted by the quantum confinement effect of thinner graphitic carbon nitride sheets and by the generated nitrogen vacancies in C-N heterocyclic units. Moreover, stronger driving force for photocatalytic H-2-evolution reaction was obtained to enhance the ability of water reduction reaction.