The Double-Row Ball Slewing Ring has three seat-rings. Steel Balls and Spacers may be poured directly into upper and nether orbits. Two rows of upper and nether Steel Balls of different diameters can be assembled according to Undertaking Power situation. The kind of open-pattern-assembly is very convenience. The load-angles of both upper and nether circular orbits are 90 degree, which enable it to undertake very large Axial Force and Tipping moment. When the Radial Force is more than 0.1 multiple of Axial Force, the orbit need to be redesigned. As the axial and radial size of this kind of slewing ring are rather big, and the structure is firm, it is especially suitable for Tower Cranes of over-medium diameter, Truck Cranes, Loading and Unloading Machines, and so on.