Ultrasound assisted extraction was used to extract tannins from Eucalyptus grandis x E.urophylla .The crude extract tannins were purified by the macroporous resin adsorption. The antimicrobial activities of tannins on multiple common bacteria were studied by using filter paper method, and the oxidation resistance of samples were studied by three different systems. Tannin in crude extract was 4.01% and increased to 53.12% when was chromatograhied by macroporous resin. Tannins had strong inhibition on the 7 kinds of bacteria activities but no distinct inhibition on Excherichia coli. Minimun antimicrobial concentration of the purified tannins on Staphyloccocus aureus、Yeast and Shigella was 1.0 g/L, and the antimicrobial activities against Live Bacillus Cereus Preparation and Salmonella were stronger than their effects against positive control. The maximum scavenging rates of crude tannins and purified tannins for H2O2 were 80.00%, 89.12% when mass concentration was 0.50 g/L, and their IC50 were 0.11 g/L and 0.12 g/L, respectively. The maximum scavenging rates of Vc , crude tannins and purified tannins for DPPH•were 98.43%, 88.97% and 92.21%. When mass concentration was 4.00 g/L, the highest scavenging rate of crude tannins and purified tannins for •OH were 87.52% and 94.32% .