We reported the possible synthesis of a new porous graphene-like carbon nitride (C6N9H3) by simply adding hydrochloric acid in the precursor of block g-C3N4. The formation of the porous graphene-like C6N9H3 can be attributed to the change in the thermal condensation modal of the precursor and the acidic condition induced by Cl− and H+. The photocatalytic activity of the samples was evaluated by the removal of NO under visible light illumination. We found that the porous graphene-like C6N9H3 exhibited enhanced photocatalytic activity compared to the block g-C3N4.We also researched the removal mechanism and found that the removal of NO in our systems was due to the synergic effect of h+ and •O2−. This study could shed light on the design of efficient photocatalysts and facilitate a deep understanding of the NO removal mechanism through photocatalytic technology.