Abstract: By transfusing dimethoate oxide into the base of chestnut trees,the authors have stu-died the transfusion and insecticidal mechanism.The result of microscopical examination on tissue slices showed that the rogor oxide was carried from the base together with the sap of the trees to the upper parts of the trees along the vascular bundles of xylem with evident directivity.The transfusion extent related to the temperature,transpiration amount of the tissue and pH value of the insecticide.