Abstract: The steadystate interaction research of calcium and zinc ions with alginate during the sol-gel transition by circular dichroism showed that this process included two phases.During the first phase before the transition point the structure of the gel-conjugate of alginate-metal ions was homological in the range of linear change.The rate and mechanism have the similar change.Molar ellipticity ［θ］^alginate_Ca at wavelength 200 nm and 205 nm，molar ellipticity ［θ］^alginate_Zn at wavelength 195 nm and 200 nm could be obtained through calculation with spectrum titration.For the same divalent cation ion，the critical sol-gel transition points were different for alginates with different compositions.