Slewing drive for solar tracking system is usually composed of single-row four point contact slewing ring, housing, worm shaft and other engineering parts. The single-row four points contact ball Slewing Bearing is composed of 2 seat-rings. It features compact in design, and light in weight. The balls contact with the circular race at four points, via which the axial force, radial force and resultant moment may be born simultaneously. It may be used for slewing conveyors, welding arms and positioners, light, medium duty cranes, excavators and other engineering machine.