The application of sodium percarbonate (SPC) catalyzed by metal-free protonated g-C3N4 under visible light (vis) irradiation was investigated for the first time to stimulate the degradation of methylene blue (MB) and tetracycline hydrochloride (TCH). The catalyst was obtained by using thermal induction polymerization and chemical exfoliation method. The structure and properties of as-synthesized samples were characterized. Moreover, the effects of various factors such as the initial solution pH on MB degradation were also evaluated. Results obtained in the test actively demonstrated that effective degradation of MB was achieved in the protonated g-C3N4/SPC/Vis system. This system has a wide range of pH application, and the catalyst presents excellent stability. Holes, superoxide anion radical (center dot O-2(-)) and hydroxyl radical (center dot OH) were confirmed as the predominant species responsible for MB degradation. The reaction mechanism for MB degradation in the protonated g-C3N4/SPC/Vis system was proposed according to the characterization of the samples, the free radical quenching tests, and electron paramagnetic resonance (EPR) spectrum analysis.