New technologies for efficient ion separation (e.g. extraction of lithium from salt lake brines) are highly desirable due to industrial and environmental concerns. A new ion concentration polarization (ICP)-based ion separation system, which is capable of extracting concentrated Li+ solutions continuously from high Mg2+/Li+ ratio brines is proposed. This system uses ICP-induced amplification of the electric field to concentrate Li+ ions and expel Mg2+, with external pressures applied to modulate the feeding flow of the brine in the microchannel and the bifurcated flow of concentrated Li+ through the branch. Through numerical simulations using a simplified two-dimensional model, effects of key operational parameters as well as same structural parameters are elaborated. It is demonstrated that the proposed system is able to continuously extract similar to 38% of Li+ from the raw brine at a fluid flow velocity of similar to 1 mm/s. The concentration of Li+ in the product solution is about similar to 13 times of the raw brine, with a Li+/Mg2+ mass ratio of similar to 10 (similar to 600 times of the raw brine). This work provides clear fundamental mechanism underlying the new method, offers important guidance for the design of relevant experiments, and paves the way for the potential industrialization of high efficiency Li+ extraction technologies.