The invention relates to a preparation method of a moistening and flavor enhancing additive agent comprising two preparation modes, wherein the mode 1 comprises the steps of firstly respectively preparing and obtaining a special tobacco extract, a seaweed extract and a vanilla extract; then mixing the special tobacco extract, the seaweed extract and the vanilla extract according to a ratio of 1:6-10:1-5, after decoloration by an activated carbon column, concentrating an effluent into a viscous fluid, thereby obtaining the moistening and flavor enhancing additive agent; and the mode 2 comprises the steps of respectively washing the seaweed and the vanilla, crushing after drying, mixing the special tobacco leaf fragment, the seaweed powder and the vanilla powder according to the ratio of 1:2-6:0.5-4, adding water, heating and reflxuing, then adding acetone, heating and refluxing, cooling, filtering, adding water or ethanol solution to a residue, continuously heating, refluxing and extracting, cooling, filtering and decoloring a concentrated solution through the activated carbon column after concentrating a filtrate, continuously concentrating the effluent into the viscous fluid, thereby obtaining the moistening and flavor enhancing additive agent. The moistening and flavor enhancing additive agent prepared by the invention not only can obviously keep the moisture of the tobacco shred, but also can enrich the flavor of the cigarette, and improve the comfortable degree of the cigarette. The cost of the invention is low, the technical process is simple, the raw material is easy to get, and the popularization and the application are convenient.