Abstract: In this paper, the gel properties of sodium alginate with Y³⁺, Ce³⁺, La³⁺ and Er³⁺ were studied. By studying the mechanical properties, equilibrium water content, ion exchange rate and gel mechanism of seaweed rare earth gel, it was found that: The coordination form of rare earth ions and carboxyl group in sodium alginate was pseudo-bridged monodentate coordination and bridge coordination. At the same time, the special three-dimensional network structure of the rare earth gel was formed through the planar and non-planar geometry formed by intramolecular and intermolecular chelation, and the gel strength of the gel formed by La³⁺, Y^{3 +}, Er³⁺, Ce³⁺ and sodium alginate M/G≈1 was between 32 and 41 N, the Young’s modulus was between 14 and 20 N, the elasticity was between 55% and 59%, the equilibrium water content was greater than 93%, the strength of the four gel was Ce³⁺> Er³⁺> Y³⁺> La³⁺, the elasticity was Ce³⁺<Er³⁺<Y³⁺<La³⁺, and the ion exchange rate was: Ce³⁺ 52.99%, Er³⁺ 50.81%, Y³⁺ 40.74%, La³⁺ 39.33%. Under different M/G ratio, the affinity between rare earth ions and sodium alginate gel was quite different: When M/G=1.99>1, the affinity of seaweed rare earth gel was in this order: Er³⁺>Ce3+>Y³⁺>La³⁺. When M/G=0.99≈1 and M/G=0.19<1, the affinity of seaweed rare earth gel was in this order: Ce³⁺> Er³⁺> Y³⁺> La³⁺. Among them, Ce³⁺, Y³⁺ and La³⁺ had a certain preference for G fragment of sodium alginate, and Er³⁺ had a certain preference for M fragment. This study would lay a theoretical foundation for the intensive processing and utilization of sodium alginate and the development of new functional materials of rare earth elements.