The invention discloses a sodium alginate / carboxylated cellulose nanocrystal hydrogel microsphere for adsorbing lead ions. The sodium alginate / carboxylated cellulose nanocrystal hydrogel microsphere comprises, by weight, 5-8 parts of sodium alginate, 6-8 parts of carboxylated cellulose nanocrystals, 0.5-0.52 parts of divinyl sulfone, 150-180 parts of distilled water and 30-40 parts of a 0.1-0.2 mol / L calcium chloride solution. The sodium alginate / carboxylated cellulose nanocrystal hydrogel microsphere has the following advantages: the sodium alginate and microcrystalline cellulose which are used as raw materials in the method are natural materials, so the microsphere is nontoxic and harmless, is friendly to the environment, and realizes appreciation and full utilization of materials as a water purifier; and the prepared hydrogel microsphere has a good homogeneity, a uniform particle size, no toxic or side effects, a large specific surface area and a large porosity, has high adsorptioncapability to lead ions and other heavy metal ions, can be used as a safe and efficient lead ion adsorbent, and has a broad industrial application prospect.