The biomass-based hydrogels can be used as the adsorbents in sewage water, and they have good adsorption capacity for heavy ions and dyes. The starch-based hydrogel was prepared with cornstarch (St) and sodium carboxymethyl cellulose (CMC) as raw materials, acrylamide (AM), acrylic acid (AA) and 2-acrylamide-2-methylpropane sulfonic acid (AMPS) as grafting monomers through grafting and cross-linking reactions and named St/CMC/P(AM-AA-AMPS). The synthesis conditions and the adsorption performances for Cu2+ were studied. The results showed that the suitable synthesis conditions were m(St):m(CMC) = 1:0.5, m(St):m(AM):m(AA):m(AMPS) = 1:3:5:2, m(St):m(APS) = 1:0.06, reaction temperature 75 °C, and reaction time 3 h. The results of adsorption experiments showed that the hydrogel had good adsorption properties for water and Cu2+. The swelling ratio was 126.77 g/g after immersed in water for 3 h. When the hydrogel was used to adsorb Cu2+ (ρ0 = 30 mg/L) in the simulated water, the removal rate of Cu2+ was 93.3%, and the adsorption capacity was 80.51 mg/g.