The polysaccharide in Gleditsia japonic.miq was researched. Based on the single factor level determination, the major factors including liquid/material ratio, extraction temperature and time were investigated by response surface analysis, and then its antibacterial activity was studied by filter paper diffusion method. The results showed that the optimum technology condition were using liquid/material at 50 mL/g, extracted at 65 ℃ for 80 min. Under these conditions, the yield of polysaccharide was (31.52±0.54) %. Furthermore, when the concentration of polysaccharide was 100 mg/mL, the antibacterial activity was in this order, S.typhimurium＜Escherichia coli＜Bacillus cereus＜Bacillus subtilis＜Staphylococcus aureus, and the minimal inhibitory concentrations of polysaccharide against Staphylococcus aureus, Escherichia coli, S.typhimurium, Bacillus subtilis, and Bacillus cereu were 25, 50, 50, 25, 50 mg/mL, respectively.