Heavy metal pollution caused by the indiscriminate disposal of toxic heavy metal wastewater has become one of the serious water environmental issues. In this study, a novel NH2-PAA/Alginate hydrogel with double network interpenetrating structure was constructed with alginate, acrylic acid, and other raw materials. Characterized by SEM, this hydrogel shows a three-dimensional porous structure, which would be useful in adsorption process for its high diffusion coefficient. The results of adsorption experimental show that the NH2-PAA/Alginate possessed the well adsorption capacity when pH above 3.5, the maximum adsorption capacity calculated by Langmuir was 176.5 mg/g, the adsorption equilibrium can be achieved within 150 min. In addition, the NH2-PAA/Alginate has good recycling ability and stability. The results of XPS analysis reveal that the Cd(II) exchanged with Ca(II) and then coordinated with amino and hydroxyl groups in NH2-PAA/Alginate. The NH2-PAA/Alginate hydrogel can deal with all kinds of heavy metal ions and is a potential material for heavy metal adsorption.