Abstract: The structure and properties of common central drainage system, the swing joint type, pivot type (static sealing structure) and flexible tubing type, used in the external floating roof steel oil tank are analyzed and compared. The authors introduce the structure and characteristics of ZYPS central drainage system applied in external floating roof steel oil tank. The actual application shows that this new type drainage system can discharge the rain water from tank top in short time, and has advantages in simple structure, high reliability, high anti-fatigue capacity, low cost and wide application scope.