The invention provides a preparation method for a banana skin drying agent and a drying mould-proof bag containing the banana skin drying agent. The preparation method comprises the following steps: cleaning and cutting the banana skin; soaking the cut banana skin into acetic acid-ethanol solution for activating; freeze-drying, crushing and screening the banana skin after being activated, thereby acquiring the banana skin drying agent. The drying mould-proof bag comprises a drying mould-proof bag body made from a breathable material, wherein the bag body is filled with the banana skin drying agent acquired according to the preparation method. The banana skin drying agent provided by the invention is natural and safe; the moisture adsorption effect is excellent; the wastes are turned into wealth; the additional value of the banana industry is increased; the banana skin drying agent is more environmentally friendly.