P-doped g-C₃N₄ has been successfully synthesized using hexachlorocyclotriphosphazene, a low cost and environmentally benign compound, as phosphorus source, and guanidiniumhydrochloride as g-C₃N₄ precursor, via a thermally induced copolymerization route. The obtained P-doped g-C₃N₄ showed excellent photocatalytic performance both in the photoreduction of H₂O to produce H₂ and the photodegradation of Rhodamine B (RhB). H₂ evolution rate on modified g-C₃N₄ reached 50.6 μmol h⁻¹, which is 2.9 times higher than that of the pure g-C₃N₄. RhB (10 mg L⁻¹) was completely photodegraded within 10 min. The structure and texture properties of the P-doped g-C₃N₄ have been investigated in detail by XRD, FTIR, TEM, EDS and STEM. With the results of XPS and ³¹P NMR, a possible existing form of P atom in the framework g-C₃N₄ has been put forward. The introduction of a P atom significantly changes the electronic property of g-C₃N₄ and suppresses the recombination of photogenerated charge carriers, thus improving its photocatalytic performance.