Searching for effective approaches of accelerating charge separation and broadening optical absorption is critical for designing a high-performance photocatalytic system. Herein, a photocatalyst based on the non-metal group doped porous ultrathin g-C3N4 nanosheets (CNB NS) was prepared through a combined methodology of precursor reforming and thermal condensation. The synergistic effect of non-metal group doping and porous ultrathin nanosheet-architecture not only endow the material with improved light harvesting and regulated band structure, but also facilitate the electron-hole pair separation, supplying numerous active reactive sites and electron diffusion channels. As a result, the CNB NS photocatalyst exhibits a highly efficient photocatalytic H2 performance (the apparent quantum efficiency is 7.45% at 420 nm) and stability in water under the visible light, which is approximately 13 times higher than that of pure g-C3N4. This study may open a new perspective for designing the non-metal group doped g-C3N4 photocatalyst and further fabricate other advanced photocatalytic materials.