In this paper, g-C3N4 and In2S3 were synthesized by thermal polycondensation and hydrothermal method, respectively. In2S3/g-C3N4 composite photocatalyst was prepared by simple mechanical grinding technology. The crystallographic structure, morphology, microstructure and optical properties of In2S3/g-C3N4 composite photocatalyst were characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), and UV visible diffuse reflectance spectrum (UV-Vis DRS). The photocatalytic activity was evaluated by degradation of tetracycline (TC) under visible light irradiation. The results show that the In2S3/g-C3N4 composite photocatalyst with grinding molar ratio of 1∶4 displays the best photocatalytic activity. The observed rate constant of TC degradation under xenon lamp is 0.025 1 min-1, which is 2.9 times and 1.6 times higher than that of In2S3 and g-C3N4, respectively. The observed rate constant of TC degradation under natural light is 0.010 4 min-1, which is 2.6 times and 1.4 times higher than that of In2S3 and g-C3N4, respectively. The superior photocatalytic performance of In2S3/g-C3N4 composite photocatalyst is attributed to the efficient migration and separation of charge carriers and the enhanced light absorption capacity. This paper provides a promising approach for designing and developing visible-light-response photocatalysts applied to antibiotic wastewater treatment.