Engineering the electronic structure of two-dimensional (2D) nanomaterials endows unique physical and chemical properties. Although developed modification strategies have significantly expanded the applications of 2D nanomaterials, exploring new strategies to regulate the electronic structure of 2D nanomaterials is also expected. Herein, we highlight a new strategy to engineer the electronic structure of 2D subnanoporous nanomaterials. As a proof of concept, based on controllable subnanopore engineering using molecular titanium-oxide incorporation, the electronic band structure of 2D graphitic carbon nitride (CN) nanosheets has been efficiently tuned with the enhancement of visible light absorption as well as separation and the migration rate of photo-excited charge carriers, exhibiting significantly improved photocatalytic activity under visible light irradiation. Our work opens a new door to engineering the intrinsic properties of 2D subnanoporous nanomaterials.