In this study, a novel zinc sodium molybdate/graphite phase carbon nitride (Na1.8Zn2.1Mo3O12/g-C3N4) heterostructure was synthesized by wet impregnation. The photocatalyst was characterized in detail from different phase purity, crystal structure, morphology, microstructure, optical properties, and showed that the preparation was successful. The effects of the loading amount of Na1.8Zn2.1Mo3O12, the initial concentration of pollutants, the amount of catalyst and the pH value on the reaction system were also discussed. The results of photocatalytic study showed that the photocatalytic activity of the synthesized Na1.8Zn2.1Mo3O12/g-C3N4 photocatalyst for tetracycline (TC) under visible light treatment was better than that of the pure g-C3N4 and Na1.8Zn2.1Mo3O12. The improved catalytic activity can be attributed to the formation of heterojunction between Na1.8Zn2.1Mo3O12 and g-C3N4 and the effective separation of photogenerated electron hole pairs. The capture tests confirmed that superoxide radical (·O2 -) and photogenerated hole (h+) are the main active species involved in the photocatalytic reaction. Finally, the possible mechanism of the synergistic effect of g-C3N4 and Na1.8Zn2.1Mo3O12 to improve the photocatalytic performance was studied.