Nowadays, the C-substitution for N in g-C3N4 can promote n-electron availability and thus considerably increase its photocatalytic properties. However, the replacement of N in triazine ring of g-C3N4 by carbon atom represents a huge challenge on account of the higher electronegativity of N over C. Herein, we firstly report a simple and effective strategy for skillfully replacing one nitrogen with carbon atom by copolymerizing n-electrons-rich uracil with dicyandiamide via a facile Schiff-base reaction. The results show that direct incorporation C4N2 ring into the framework not only maintains the structural features of g-C3N4 and narrows its bandgap from 2.75 to 2.58 eV, but also effectively boosts the dissociation of photogenerated excitons. Consequently, C-incorporated g-C3N4 could harvest more solar light (lambda = 750 nm). As expected, the photocatalytic hydrogen evolution rate of the optimal C self-doped g-C3N4 is almost as high as 13 and 20 times that of bare g-C3N4 under the visible-light exposure and the blue light illumination, respectively. Most importantly, the optimal sample also shows excellent performance under the green (lambda = 500 nm) and yellow (lambda = 550 nm) light illumination (94.07 and 28.47 mu mol g(-1) h(-1), respectively). This work sheds light on a subtle molecular-tailored protocol for controlling carbon self-doping site of the g-C3N4 to optimize the intrinsic electronic properties and photoactivity.