Polysaccharide-based hydrogels containing specific hydrophilic groups can adsorb dyes in water. Using a polysaccharide derivative (carboxymethyl starch sodium, CMS) as raw material, acrylamide (AM) and acrylic acid (AA) as grafting monomers, a polysaccharide-based hydrogel CMS/P(AM + AA) was synthesized. The structure of the hydrogel was characterized by FT-IR, SEM and TGA. It was found that carboxyl, amino and amide groups appeared in the molecular chains of the product. The absorption performances of the hydrogel for water and methylene blue (MB) in water were tested. It was found after soaking in water for 2 h, the swelling rate of the hydrogel was 86.55 g/g. The adsorption process of MB by CMS/P(AM + AA) conformed to the Langmuir model and belonged to the homogeneous surface adsorption. At 25 ℃, the adsorption capacity of CMS/P(AM + AA) was 1642.14 mg/g. After 4 times of acid washing regeneration, the removal rate of MB could still reach 78.5%.