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］alginateCa at wavelength 200 nm and 205 nm，molar ellipticity ［θ］alginateZn 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.