The invention discloses an edible sweet film and a preparation method thereof and belongs to the technical field of food packaging and protective materials. According to the preparation method, chitosan and whey protein are used as film forming base materials, xylooligosaccharide is used as a sweetener and genipin is used as a crosslinker. A film forming liquid of the edible sweet film contains the chitosan and whey protein. In the invention, the chitosan and the whey protein are compounded creatively with addition of the crosslinker, so that the film remains the nutrients in the whey protein. The film has good insulation property, mechanical performance and long-acting antibacterial performance. The raw materials of the edible sweet film are all edible, wherein a chitosan acetic acid solution has a sour taste while the xylooligosaccharide enable the film to have a sweet taste, thereby forming the edible sweet film. The method is simple in operations and low in cost, and has a wide application prospect in food industry.