The invention discloses a Flos Caryophylli extractive, which is prepared by the following steps: (1) drying the Flos Caryophylli leaves at 40-65 DEG C, and crushing; (2) adding 95% ethanol according to the weight to volume ratio of 1: 3-9, conducting microwave treatment while electric heating at 500-600 W for 70-120 s, and filtering to obtain a filtrate; (3) adding 95% ethanol according to the weight to volume ratio of 1: 3-9, soaking 4-6 d, and filtering to obtain a filtrate; (4) adding 95% ethanol according to the weight to volume ratio of 1:3-9, conducting ultrasonic extraction with power of 500-650W for 1-1.5 h, and filtering to obtain a filtrate; and (5) merging the filtrates obtained in the step (2), (3) and (4), concentrating at 40-55 DEG C and 400-600 mm of mercury column to obtain an extract. The invention also discloses the application of the extractive to control of tobacco bacterial wilt disease. The invention can inhibit the growth of Pseudomonas solanacearum; after treatment by the extractive, Ralstonia solanacearum flagella disappear and the thalli are digested, so as to inhibit thalli protein synthesis, and reduce POD, CAT and SDH enzyme activity. In addition, control effect of tobacco bacterial wilt in greenhouse and field reach 71.5% and 59.7% respectively, therefore the invention has great application value.