Compared the antibacterial activities of three phenolic acids (gallic acid, protocatechuic acid, and chlorogenic acid) against S. putrefaciens, and investigated the antibacterial effects of gallic acid on S. putrefaciens by means of scanning electron microscopy, flow cytometry, cell membrane integrity and permeability measurement. The results showed that gallic acid had the strongest antibacterial activity against S. putrefaciens among the three phenolic acids, and its minimal inhibitory concentration and minimal bactericidal concentration were 1.25 mg/mL and 2.5 mg/mL, respectively. After treatment with gallic acid at the minimum inhibitory concentration, the cell morphology of S. putrefaciens changed with obvious depression on the surface. The apoptotic rate increased significantly. The leakage of nucleic acid and protein increased, and the integrity of cell membrane was destroyed. The permeability of cell membrane increased, and a large amount of intracellular electrolytes leaked into the culture medium.