We report a simple strategy for realizing the tunable structure distortion of graphitic carbon nitride (g-C3N4) layers by H2 post calcination to improve the intrinsic electronic structure and the photocatalytic performances of g-C3N4 samples. In comparison with the O2 or N2 post treatment, the H2-modified g-C3N4 develops new optical absorption above 460 nm and enhances photocatalytic activity for NO removal. The combined characterization results reveal that H2 heating induced the structure distortion of g-C3N4 layers is originated from the creation of amino groups within the structure and generation of the strong hydrogen bonding interactions between layers. The distorted structure allows n–π* electron transitions in g-C3N4 to increase visible-light absorption. The structure distortion also enables more electrons to be available for initiating the photocatalytic reaction and the separation of photogenerated charge carriers in g-C3N4. This work provides a simple strategy for realizing the tunable structure distortion of g-C3N4 layers to adjust its electronic structure and photocatalysis.