Herein, self-supported oxygen-doped carbon nitride aerogel (OCNA) was successfully fabricated through a facile self-assembly method combined with hydrothermal process, without adopting any harmful solvents or cross linking agents. The fabrication mechanism of OCNA was discussed. OCNA exhibited much faster charge separation efficiency, longer carriers' lifetime than bulk carbon nitride (BCN). More importantly, oxygen-doping led to a more negative conduction band (CB) position and narrower band gap (E-g). Hence, the spectral response range of OCNA was extended dramatically and the hydrogen evolution rate (HER) of OCNA (lambda > 510 nm) was about 26 times as high as that of BCN prepared herein. OCNA exhibited a remarkable apparent quantum yield (AQY) of 20.42% at 380 nm, 7.43% at 420 nm and 1.71% at 500 nm, superior to most of the reported C3N4-based materials. This work paves a facile colloid chemistry strategy to assemble self-supported 3D CNA that could be widely adopted in the sustainability field.