Aiming at the problem that SO₄^2-,Ca²⁺,Mg²⁺ and other impurity ions need to be removed in the process of direct alkali production from saturated brine,a new process for separating and refining saturated brine with nanofiltration membrane was explored.By examining the flux and ions rejection rate of three types of NF270,DL2540 and ESNA1 nanofiltration membranes,DL2540 was chosen as the experimental membrane.The effects of DL2540 nanofiltration membrane on ions rejection rate,separation performance of saturated brine from salt field and the refining effect of saturated brine were analyzed respectively.The results showed that increasing the concentration of the ions and reducing the pressure was beneficial to the separation of cations and anions with different valences.The rejection rates of SO₄^2-,Ca²⁺ and Mg²⁺ in the saturated brine of salt field reached 95% above,30%~50% and 30%~70%,respectively.The rejection rates of DL2540 nanofiltration membrane on Na⁺ and Cl^- were both lower than 15%,which further proved that DL2540 nanofiltration membrane has better stability and divalent ions rejection effect,and showed promising application prospect in saturated brine purification.