The invention relates to the field of polymers, and in particular relates to a blue fluorescent polymer, blue fluorescent powder, blue fluorescent fibers, ultraviolet conversion into blue light resinas well as preparation methods and applications of the blue fluorescent polymer, the blue fluorescent powder, the blue fluorescent fibers and the ultraviolet conversion into blue light resin. The bluefluorescent polymer is prepared by performing modification on a maleic anhydride copolymer with a special general formula by a strong alkali; and the aqueous solution or the aqueous dispersion liquidof the blue fluorescent polymer has an excitation range from 300 to 425 nm, an emission range from 400 to 550 nm, and an emission peak of 430-520 nm of a blue light region. The blue fluorescent polymer, blue fluorescent powder, blue fluorescent fibers and ultraviolet conversion into blue resin provided by the invention have the advantages of high fluorescence intensity, low raw material costs, amature production process, no biological toxicity or environmental pollution, good water solubility or water dispersion, fluorescence performance which is not restricted by a solution concentration and a solid form, various application forms, a simple preparation method easy to implement and extremely-easy industrial promotion; and the blue fluorescent polymer, the blue fluorescent powder, the blue fluorescent fibers and the ultraviolet conversion into blue resin have broad application prospects in the fields of anti-counterfeiting technologies, biological imaging, light-transfer films, solarcell sealants and fluorescent dyes.