The invention discloses a prevention preparation for tobacco weather fleck and a use method. The prevention preparation is characterized in that the prevention preparation is prepared by dissolving monopotassium phosphate, salicylic acid and kasugamycin in water according to a mass ratio of 25-50:1-4:25-50 to prepare a mother solution and then diluting by water. The method comprises the steps of in 50-60 days after the tobacco is transplanted, spraying the prevention preparation to the front and back surfaces of the tobacco after raining. The prevention preparation for tobacco weather fleck and the use method have the advantages that by applying the prevention preparation, tobacco nutrition can be balanced, an oxidation resistance of cells is enhanced, and a better prevention action against other tobacco diseases caused by intrusion of pathogenic bacteria after the tobacco is damaged by O3 is realized. Compared with the prior art, the prevention preparation has the advantages of simpleness in manufacturing, convenience in use and stable prevention effect.