Molybdenum disulfide (MoS₂) was synthesized via hydrothermal process under the assistance of citric acid, which exhibited high photocatalytic property in the application of methylene blue (MB) degradation. The flower ball microstructure of MoS₂ changed with different amounts of citric acid. X-ray diffraction (XRD), Scanning electron microscope (SEM), UV-Vis diffuse reflectance spectra have been employed to characterize the samples. It improved the photocatalytic efficiency nearly 19.77% compared to MoS₂ without citric acid. When H₂O₂ was added, the synergistic effect of MoS₂ and hydrogen peroxide (H₂O₂) was observed in photocatalytic reaction system, which degraded MB completely within 40 min under visible light irradiation.