The invention discloses a preparing and use method for an additive capable of improving the quality of flue-cured tobacco leaves in a tobacco leaf modulation stage. The additive uses fresh tobacco leaves as a raw material and is prepared through a membrane separation method. In the tobacco leaf modulation stage, water is added in the additive, the additive is diluted into a solution with the concentration of 10-15%, the solution is added on surfaces of normal mature fresh tobacco leaves, and then the fresh tobacco leaves are dried in air, and baking is performed according to a normal three-stage baking technique. The invention further provides a development utilization method for inapplicable fresh tobacco leaves, the development utilization method uses the inapplicable fresh tobacco leaves as a raw material, and the additive capable of improving the quality of the flue-cured tobacco leaf in the tobacco leaf modulation stage is prepared through the membrane separation method. The preparing and use method can turn the inapplicable fresh tobacco leaves into a valuable material and uses the tobacco waste resource as the raw material, is rich in raw material source, and is low cost; the preparing method is easy to operate, and the prepared additive has good compatibility with the tobacco leaves. The hierarchal structure of the flue-cured tobacco leaves is remarkably improved through additive spraying, aroma substances such as organic acids and polyphenol are increased, the smoking quality is improved, and indexes such as aroma amount and offensive odor can be remarkably improved.