Abstract: In order to evaluate the application potential of tetraconazole in the prevention and control of tobacco powdery mildew, the spore germination method was used to test the toxicity of tetraconazole on spore germination of Golovinomyces tabaci, and its effect on the microscopic morphology of G. tabaci. The pot experiments were conducted to test the control effect of tetraconazole on tobacco powdery mildew in the greenhouse. The results indicated that tetraconazole had a strong inhibitory effect on conidial germination of three G. tabaci strains, and the EC₅₀ values were 0.3422, 0.3561 and 0.4105 μg/mL, respectively. The EC₅₀ values for inhibition of germ tube elongation were 1.7466, 1.3988, and 1.3229 μg/mL, respectively. Microscopic observation results indicated that tetraconazole had no teratogenic effect on conidia, but it could make the primary hyphae thickened and bifurcated. The results of the greenhouse control test showed that after 14 days of treating tobacco seedlings with 4% tetraconazole water emulsion at doses of 1.61, 3.22, and 5.36 g/L, respectively, the protective effect ranged from 76.62% to 95.67%, and the therapeutic effect ranged from 71.42% to 90.91%.