Oregano oil microcapsule was prepared by utilizing sodium alginate as wall materials. The technology of preparing oregano oil microcapsule was optimized by orthogonal experiment design, and its structural characterization and antimicrobial activity were also tested. The results showed that oregano oil microcapsule shows the best quality when the concentration of sodium alginate, calcium chloride, Tween-80 and monoglycerides were 2.5%, 1.5 %,0.2% and 0.1% respectively, and the ratio between wall and core materials was 1∶1. The embedding rate was 60.48% under the condition. There are vesicular structures in the internal of the prepared oregano oil microcapsule, which showed obvious antimicrobial activity, and the inhibition zone diameter of Botrytis cinerea arrived at 90 millimeters when the addition amount of oregano oil microcapsule achieved 0.02 gram.