Abstract: Study on the colonization of Trichoderma in the soil and the effect of Trichoderma preparations on the amount of soil microorganism by dilution isolation. And the control effect of Trichoderma preparation on jasmine southern blight was tested in field. The results showed that, in the case of containing substrate, the amount of Trichoderma in the soil was tended to increase first and then decreased. The amount of Trichoderma in sterilized soil was significantly higher than that in natural soil. The number of bacteria and fungi were increased significantly in the jasmine rhizosphere when the Trichoderma preparation was applied to jasmine plantations, and the incidence of jasmine southern blight was significantly reduced. The highest control efficiency was reached to 71.07%.