Improving visible light utilisation and suppressing the rapid complexation of photogenerated carriers is a major challenge for the efficient activation of graphite-phase carbon nitride (g-C3N4) for the degradation of pollutants by peroxynitrite (PMS). The interfacial interaction between P-doped g-C3N4 nanosheets (PCN) and cobalt phthalocyanine (CoPc) was enhanced to achieve efficient activation of PMS for tetracycline (TC) degradation. PCN was prepared from urea and sodium hypophosphite by high temperature phosphating process, and then calcined with CoPc in muffer furnace to construct heterojunction. The results showed that the construction of the heterojunction not only extended the light absorption edge to the visible light region, but also made the degradation rate of TC(10 mg/L) reached 98.8% after 40 minutes in 50 mL solution activated by 20 mg of optimal catalyst and 30 mg of PMS, and the degradation rate was 0.087 min-1. This is due to the heterojunction potential at the interface between PCN and CoPc accelerating the separation of photogenerated carriers. At the same time strong interfacial interactions provide channels for electron transfer, allowing the reduction of O2 to generate large amounts of ?O2? radicals and activation of PMS to generate ?SO4? and ?OH radicals to degrade TC.