Herein, Zn₃In₂S₆ photocatalyst with (110) exposed facet was prepared by low temperature solvothermal method. On this basis, a highly efficient binary Zn₃In₂S₆/g-C₃N₄ was obtained by low temperature solvothermal method and applied to the degradation of tetracycline (TC). The samples of the preparation were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, UV–vis diffuse reflection spectroscopy, and photoluminescence spectroscopy. Furthermore, the degradation performance of photocatalysts on TC was investigated under different experimental conditions. Finally, the mechanism of Zn₃In₂S₆/g-C₃N₄ composite material degrading TC is discussed. The results show that Zn₃In₂S₆ and Zn₃In₂S₆/g-C₃N₄ photocatalysts with excellent performance could be successfully prepared at lower temperature. The Zn₃In₂S₆/g-C₃N₄ heterojunction photocatalyst could significantly improve the photocatalytic activity compared with g-C₃N₄. After 150 min of illumination, the efficiency of 80%Zn₃In₂S₆/g-C₃N₄ to degrade TC was 1.35 times that of g-C₃N₄. The improvement of photocatalytic activity was due to the formation of Zn₃In₂S₆/g-C₃N₄ heterojunction, which promoted the transfer of photogenerated electron–holes. The cycle experiment test confirmed that Zn₃In₂S₆/g-C₃N₄ composite material had excellent stability. The free radical capture experiment showed that ·O₂⁻ was the primary active material. This study provides a new strategy for the preparation of photocatalysts with excellent performance at low temperature.