Double-row unequal-diameter ball slewing bearing consists of upper and lower row balls, inner and outer rings, separators, grease and sealing device. Balls and separators could be carried to upper and lower raceways directly. According to load conditions, there fit upper and lower, two rows balls with different diameters. In order to make slewing bearing a complete part before mounted on the main frame, we need to use several joint bolts connecting up and down rings. To adjust the clearance of slewing bearing, the clearance is fixed by grinding ends when slewing ring is assembled. Such open mode fitting features extraordinary convenience. Load angles of upper and lower round arc raceways are both 90° and can bear large axial force and tilting moment. When radial force is 0.1 times greater than axial force, the raceway needs special design. Double-row unequal-diameter ball slewing bearing is particularly suitable for towel crane, mobile crane and other loading machinery which require working diameter above medium range.