The invention discloses modified polysaccharide with a fluorescent property as well as a preparation method and an application thereof. Fluorescence groups containing perylene structures are introduced in the acylation process through hydroxyl groups periodically distributed on a macromolecular chain of polysaccharide (starch, glucan, chitosan, chitin, alginic acid, cellulose and cellulose derivatives, so that the function of isolation of the fluorescence groups is achieved, an ACQ (aggregation-caused quenching) phenomenon of perylene type fluorescent molecules is eliminated, and accordingly, low-cost, efficient and practical modified polysaccharide with the fluorescent property is obtained. A fluorescent material prepared from the modified polysaccharide maintains the fluorescence characteristic of perylene light functional groups, has excellent properties of polysaccharide macromolecular materials, can be easily processed and formed, can be manufactured in various forms such as films, fiber, coatings, microspheres, micelle and the like, and has important practical value in fields of films, fiber, coating, ink, dye and the like.