To select suitable nanofiltration membrane for seawater softening, the main ions rejection performance of the three famous brand nanofiltration menbranes NF270, ESNA, DK were done in the condition of simulated BoHai seawater. The results show that the membranes NF270 and ESNA have low rejection of divalent ions, they can’t separate monovalent ion from divalent ion effectively. The DK membrane can separate monovalent ion from divalent ion effectively, and the rejection rate of divalent ions is above 92%, the rejection rate of monovalent ions is below 30%, the rejection rate of TDS is about 38%. So the nanofiltration membrane of DK is suitable for the pretreatment of SWRO for effectively reducing the desalination fouling risk and improving system recovery.