In this paper, a series of m-SCCN composite photocatalytic materials were prepared by direct calcination using strontium carbonate (SrCO3) and melamine (C3H6N6) as raw materials. The photocatalytic degradation effect of m-SCCN composites prepared by different raw material ratios, different calcination temperatures and different calcination time on crystal violet solution under visible light was studied. The materials were characterized by SEM, XRD, UV-Vis and so on. The results show that the treatment effect of crystal violet is best when SrCO3∶C3H6N6 is 7%(w/w), calcination temperature is 600 ℃, and calcination time is 4 h. The removal rate can reach 89.70% after 120 min of light, which is 5 times that of pure g-C3N4 (17.70%). The analysis mechanism may be that SrCO3 destroys part of the hydrogen bonds in the g-C3N4 plane, resulting in the ring opening of the hepazine unit to generate a strong electron-withdrawing group-cyano group (-C≡N), which changs the transmission path of photogenerated electrons. The separation efficiency of photogenerated electrons and holes optimizes the photocatalytic activity of m-SCCN.