In order to solve the problem of heavy metal pollution, the gel was formed by crosslinking sodium alginate with calcium ion, and the gel was prepared into ultralight sponge by vacuum freeze-drying. The experimental results showed that the natural polysaccharide alginate dissolution process, the microstructure first gradually extended from the filamentous structure to the lamellar structure, while the alginate gel sponge formed a dense porous structure and the microstructure changed. The cross-linking ratio of sodium alginate to calcium chloride is 1:1, the specific surface area of the resulting gel reaches 2.1543 m2/g. The saturated adsorption capacity of alginate hydrogel to Cu2 and Pb2 reached 29.2 and 90.22 mg/g at pH=3, respectively. The maximum adsorption of Cu2 and Pb2 reached 87.7 and 240.8 mg/g. When the adsorbent addition amount was 50 mg. When the adsorption temperature is 40 ℃, the adsorption capacity of Cu2 and Pb2 reaches the maximum, and the adsorption capacity is 29.4 and 89.6 mg/g. The adsorption rate experiments showed that equilibrium adsorption of Cu2 and Pb2 was achieved at 50 min with adsorption capacity of 30.2 and 89.7 mg/g.