Abstract: In this paper, the saturation and release properties of nuclear grade lithium mixed bed resins used in the chemical and volume control system（RCV） of nuclear power plant, i.e. the reciprocal transformation relationship between resin hydroxide ion（OH-） and borate ion, are studied, and simulated tests such as the relationship between boron saturation and boron concentration, the influence of different velocity, and the leaching release and re-absorption of saturated resin boron were carried out. The result shows that the boron saturation of ion exchange resin is a dynamic equilibrium, and boron will be absorbed or released with the change of boron concentration in the system; and the change of velocity in a certain range do not cause obvious change to the boron saturation equilibrium time and exchange capacity of resin.