Abstract: In order to clarify the migration and degradation of metalaxyl, oxadixyl and dimethomorph from soil to tobacco leaves and their distribution characteristics in different parts of leaves, the effects of root irrigation application methods on pesticide residues in tobacco leaves were studied by GC-MS/MS. The results showed that the residues of the three pesticides in soil decreased gradually after root irrigation, and the degradation dynamics accorded with the first-order kinetic equation. The residues in different parts of tobacco plants showed the trend of lower leaves > middle leaves > upper leaves. The pesticide residues of metalaxyl and dimethomorph in tobacco leaves were lower than the maximum residue limit on the 7th day after application, and the pesticide residues of oxadixyl in tobacco leaves were still higher than the maximum residue limit on the 28th day after application. It can be seen that the risk of metalaxyl and dimethomorph overrun in tobacco leaves was lower, and the risk of oxadixyl overrun was higher after the recommended high dose of root irrigation.