Abstract: In order to explore the antibacterial activity of emodin against Escherichia coli（E.coli）and its antibacterial mechanism, the experiment was conducted to study the antibacterial activity of emodin against E.coli by measuring the minimum inhibitory concentration（MIC） of emodin against E.coli and the antibacterial activity. By measuring the changes in the conductivity of the bacterial solution, the content of macromolecular substances, the concentration of calcium ions, the total leakage rate and the content of alkaline phosphatase before and after the action of MIC,0.5 MIC emodin and E.coli,the antibacterial mechanism of emodin against E.coli was preliminarily explored. The results showed that emodin had obvious antibacterial activity against E.coli,and its MIC was 64 μg/mL;the conductivity of E.coli bacteria liquid, the content of macromolecular substances, the concentration of calcium ions, the total leakage rate and the content of alkaline phosphatase were significantly higher than that of the control after the action of MIC, 0.5 MIC emodin and E.coli for 1-8 h（P＜0.01）. The results suggested that emodin could increase the permeability of the E.coli cell membrane and cell wall, so that a large amount of substances in the E.coli bacteria could be leaked out, thereby achieving in vitro antibacterial activity.