Abstract: To investigate the mechanisms underlying the reversal of cell polarity, a mathematical model consisting of a pair of reaction-di usion equations was presented and solved numerically with the Lattice—Boltzmann method. It was found that, by applying a reversal gradient of Rac signal in a cell, labels for lamellipod (i.e., PI3K, and PIP₃) would disappear from the front of cell, and redistribute to the rear, while labels for tail (i.e., PTEN, PIP₂) would act oppositely. The spatiotemporal patterns of lamellipod and tail interconversion derived from our numerical simulation agreed well with that of the experimental observations. Besides, the time delay taking place between actin assembly at the new front and disassembly at the previous front was medicated by the completion of an activator (i.e., PI3K), without the help of a supposed "global inhibitor".