The invention relates to a method for preparing regenerated cellulose spherical aerogel modified through carboxylation, which aims at the problem of poor adsorptive property of the cellulose aerogel prepared by the existing methods. The method comprises steps of firstly, mixing sodium hydroxide, urea and deionized water, then adding into a cellulose raw material, preparing a cellulose solution, adding the cellulose solution into a regeneration solution for solidifying, washing and obtaining spherical hydrogel; and secondly, dissolving TEMPO (tetramethyl-piperidin-1-oxyl) and sodium bromide into deionized water, adding the spherical hydrogel, then adding a sodium hypochlorite solution, regulating pH value of a system through a sodium hydroxide solution, steeping, exchanging the collected solid phase objects sequentially through absolute ethyl alcohol and a tertiary butanol solvent, then cooling, finally, freeze drying so as to finish preparing the cellulose spherical aerogel. The largest capacity of the obtained spherical aerogel in adsorbing metal ions Cu<2+> reaches 0.55m mol / g, and the adsorptive property is good.