By the experimental investigation of homogenization treatment of 2091 Al-Li alloy with an electric field, we find the abnormal phenomena of diffusion of solute atoms with an electric field. The results show that the dissolution of second phase particles is promoted by means of the vacancy mechanism because the diffusion coefficient of the solute atoms is greater than that of the vacancy-solute complexes at the beginning of the homogenization treatment. Increasing the homogenization time with an electric field, the diffusion coefficient of vacancy-solute complexes is raised, whereas that of solute atoms is reduced because of the decreased potential energy of second phase at grain boundaries. Therefore, the nonequilibrium segregation of Cu elements is generated near the surface of the ingot by the complex mechanism. By way of the experimental study of the soluting treatment with an electric field, the nonequilibrium segregation of Li is induced at grain boundaries responsible for the delta precipitates.