Abstract: In view of seawater softening for offshore oil-fields water injection，a pilot study of seawater softening was done in Jiaozhou bay using ultrafiltration (UF)-nanofiltration (NF) integrated techniques. The effect of pressure on the performance of two nanofiltration membranes was investigated，also the quality and compatibility of permeate water were analyzed when the recovery of nanofiltration was 70%. Long-term experiment on NF-A nanofiltration membranes was carried out. The result showed that the permeate water of NF-A could be compatible with the formation water. UF-NF integrated membrane technique can stably provide water of high quality to offshore oilfields for a long time.