In order to explore the role of pmrA gene in acid tolerance resistance and biofilm formation of Salmonella typhimurium(S. typhimurium) induced after acid stress. Measuring the growth curve， acid tolerance response， and biofilm formation ability of the wild-type (WT) strain of S. typhimurium and pmrA deletion mutant strain (ΔpmrA) to preliminarily confirm whether acid stress and the lack of pmrA affect the biofilm formation ability of S. typhimurium. Further determined the strain characteristics of WT and ΔpmrA such as swimming ability， surface hydrophobic ability and self-aggregation. At the same time， metabolic activity， extracellular polymeric substance (EPS) content and biofilm microstructure of the biofilm formation also should be analyzed to explore the mechanism of pmrA deletion on the biofilm formation ability of acid stressed S. typhimurium. The result: After acid stress， the acid tolerance of ΔpmrA was 53.92 % of WT. On the 4th day of biofilm culture， the biofilm formation of ΔpmrA was only 54.68% of WT. The swimming ability and hydrophobicity of ΔpmrA were 35.20% and 59.10% of WT， respectively. After acid stress， the biofilm metabolic activity and the extracellular polymeric substances content of ΔpmrA were increased to a certain extent compared with those which had not experienced， however， they were dramatically lower than those of the WT strain(P<0.05). In the meantime， the three-dimensional structure of the biofilm of the ΔpmrA was still relatively scattered and the number of living cells in the membrane were prominently less than the WT strain (P<0.05). Conclusion: pmrA gene was closely associated with S. Typhimurium， especially in acid tolerance response and biofilm formation.