Abstract: In order to save fresh water and expand the use of seawater, thermo-chemical seawater washing for oily sludge disposal was investigated. It was observed that the dried oily sludge from a crude oil tank, which contains 9.8% moisture, 25.6% oil and 64.6% solid, could not be well disposed directly by thermo-chemical washing, when sludge was not pre-extracted. The extraction solvent was naphtha (such as 120# solvent naphtha), and the oil content of the extracted sludge was about 18.8% (dry basis). Seawater was more effective than fresh water during the washing process. The proper washing liquid was seawater with 10 g/L nonylphenol polyeothoxylates (e.g.TX-10). With a mass ratio of liquid to extracted sludge of 5, operation temperature of 60 ℃, stirring rate of 180 r/min and stirring duration of 30-40 min, the oil content in the sludge washed once was about 2.80% (dry basis), and that in the sludge washed twice was about 0.23% (dry basis), which was less than the oil control limit of 0.30% (dry basis) for mud discharge according to China's national standard GB 4284-1984, “Contaminant Control Standard of Sludge for Agriculture in China”. Moreover, in the experiment on reuse of washing wastewater, 1 g of TX-10 was added per liter of waste water in order to maintain washing efficiency. The technique with solvent extraction and seawater washing is efficient for dried oily sludge of tank bottom, and has a prospective application on the fields of seawater direct use and oily sludge disposal.