The formation of heterojunctions is an efficient strategy to extend the light response range of TiO₂-based catalysts to the visible light region. In addition to the bandgap edge match between the narrow bandgap semiconductors and the TiO₂ substrate, a stable phase interface between the sensitiser and TiO₂ is crucial for the construction of heterojunctions, since it acts as a tunnel for the efficient transfer of photogenerated charges. Herein, the coincidence site density (1/Σ) of graphite-like carbon nitride (g-C₃N₄) nanoflakes and two types of TiO₂ nanofibres [anatase and TiO₂(B)] was calculated by near coincidence site lattice (NCSL) theory. It was found that the coincidence site density of g-C₃N₄ and TiO₂(B) nanofibre with an exposed (001) plane is 3 times of that of the g-C₃N₄ and anatase nanofibre with exposed (100) plane. This indicated that the g-C₃N₄ nanoflakes are more favoured to form stable heterojunctions with TiO₂(B) nanofibres. As expected, a stable phase interface was formed between the plane of (22–40) of g-C₃N₄ and the plane (110) of TiO₂(B) which had same d-spacing of 0.35 nm and the same orientation. Under visible light irradiation, the photogenerated electrons could efficiently migrate to the TiO₂(B) nanofibres from the g-C₃N₄ through the heterojunctions. So the g-C₃N₄/TiO₂(B) system exhibited better photodegradation ability for sulforhodamine B (SRB) dye than the g-C₃N₄/anatase system, although the photoactivity of the anatase nanofibres was much better than that of the TiO₂(B) nanofibres.