A new type of boron-doped graphitic carbon nitride (B-g-C3N4) nanosheets was prepared by a benign one-pot thermal polycondensation process. Systematic studies revealed that a B-doping amount of 1 at% into g-C3N4 (1at%B-g-C3N4) showed the best photocatalytic H2 evolution activity of 1880 μmol h-1 g-1 under visible light irradiation (>400 nm), which is more than 12 times that of the pristine g-C3N4 bulk. Detailed characterizations revealed that the high photocatalytic performance could be attributed to the combination of band structure engineering and morphological control. B-doping not only reduces the band gap to absorb more visible light but also exhibits a higher surface area of B-g-C3N4 (49.47 m2 g-1) as compared to that of g-C3N4 bulk (8.24 m2 g-1), which subsequently improve the photocatalytic performance drastically. This work demonstrates a synergistic strategy to prepare efficient metal-free B-g-C3N4 nanosheets as a promising photocatalyst for H2 evolution under visible light with good stability.