The invention discloses a preparation method and applications of carboxylation chitosan. The preparation method comprises following steps: a dimethylsulfoxide solution of glutaric anhydride is delivered into a sealed reactor, and is heated, chitosan is added for reaction, an obtained product is reacted in sodium hydroxide solution so as to obtain carboxylation chitosan; carboxylation chitosan is dissolved in a solid acid solution, calcium chloride is added for dissolving, an obtained mixture is subjected to spray drying so as to obtain carboxylation chitosan hemostatic particles; carboxylation chitosan is dissolved in the solid acid solution, calcium chloride is added for dissolving, the obtained mixture is subjected to freeze drying so as to obtain carboxylation chitosan hemostatic sponge; carboxylation chitosan is dissolved in an acid solution, an obtained mixed solution is injected into a mould, the mould is sealedly coated with a one-way permeable membrane, and is immersed in an alkaline medium so as to obtain chitosan gel, the obtained chitosan gel is washed with deionized water until pH value reaches 7, and is immersed in a calcium chloride solution for crosslinking, an obtained product is collected, washed, immersed in a glycerine solution, collected, and drained, is added into absolute ethyl alcohol for single-surface steaming, and is dried so as to obtain carboxylation chitosan hemostatic membranes.