The solute redistribution during the solidification of ternary alloy was theoretically studied through thermodynamic and kinetic analyses. The mathematical models for the solute partition at the growth interface and the solute redistribution in the directional solidification of a ternary alloy are established. The results show that the solute partition at the growth interface of ternary alloys depends on the interface diffusion coefficient, growth rate, as well as the solute partition ratios of the two binary subsystems. The solute distributions in directionally solidified ternary alloy samples are calculated, from which the path for the interface composition variation is obtained.