The triazine-based carbon nitride known as polytriazine imide (PTI) is a metal-free semiconductor photocatalyst but usually shows moderate activity due to its limited charge transfer mobility. Here, carbon self-doped PTI (C-PTI) was prepared via a facile and green method by using glucose as the carbon source. In the condensation process, glucose can promote nanotube formation, giving the product larger surface areas. Moreover, carbon self-doping induces an intrinsic change in the electronic structure, thus optimizing the band structure and the electronic transport property. Therefore, the as-synthesized C-PTI exhibits remarkably enhanced photocatalytic activities for both hydrogen evolution and tetracycline degradation reactions.