Abstract: This paper describes the process characteristics and washing principle of Crude Oil Washing System technology (COWS), introduces its application in 50 000 m³ oil tank of Weizhou Terminal Treatment Yard and analyzes the technical issues existed in the washing operation. The washing result shows that this technology not only by all means washes oil tank (98% organic deposition is recovered to standard crude oil based on jetting, disintegration and resolution), but also meets the needs of safety, health and environmental protection with time-saving way.