In order to improve the mechanical properties of sodium alginate (SA) fibers, the low-temperature dissolution method was used to dissolve high-quality SA. During the wet spinning process, the coagulation conditions were changed and the diffusion coefficients corresponding to different coagulation times, temperatures and concentrations were calculated based on Fick's law of diffusion to explore the diffusion kinetics of multiple ions. The effects of the coagulation time, temperature and concentration on the mechanical properties, crystallization properties, thermal properties and morphology of the fibers were studied. The study of diffusion kinetics shows that the diffusion of multiple ions in a low-temperature dissolution system is ordered. Ca²⁺ preferentially exchanges with Li⁺ and then with Na⁺ to form Ca²⁺ cross-linking points inside SA fibers. The increase of the coagulation time, temperature and concentration can promote double diffusion to varying degrees, increase the degree of crosslinking, and improve the mechanical properties of the fiber. When the coagulation time is 15 min, coagulation temperature is 35 °C, and coagulation concentration is 2%, the breaking strength of the fiber is 4.01 cN dtex⁻¹ and the elongation at break is 11.39%. Compared with the SA fiber prepared under the original conditions, the increase is 64.34% and 68.74%, respectively. This experiment provides a theoretical basis for the preparation of SA fibers, membranes and other hydrogel products with excellent performance by in-depth study of the diffusion kinetics in the multi-ion diffusion process under the low-temperature dissolution system.