Abstract: In an FPSO sewage tank of Bohai Oilfield, a special sediment will form on the bilge and the bulkhead of the ship after along period of storage. The sediment is hard, which is difficult to remove manually and cannot be dissolved by conventional solvent, acid or alkalis. In order to efficiently remove the sediment in the sewage tank, we use SEM, EDS and XRD to analyze the main component of this special sediment assecondary clay minerals. Through the immersion and disintegration test of the sediment, three new dispersants have been developed, which can disperse these diment better in the dissolution test. Combined with the test results, the staff study the formation mechanism, and a treatment technology for this special sediment is proposed, which can reduce the difficulty and intensity of manual cleaning operations and avoid personnel injuries. It can be applied to the sediment cleaning in the case of inconvenient opening of the sewage tank.