The double rowl slewing bearing has two row steel balls for structure, it has bigger load capacity comparing to single row type slewing bearing and better safety factor, and it could bear axial load, radial load and tilting moment at the same time. Double row ball slewing ring has three seat rings, the steel ball and the spacing block can be directly arranged into the upper and lower races, two rows of upper and lower steel balls with differently diameter are fitted according to the stress condition. Double row different ball slewing bearing ring’s axial and radial size are relatively large and solid in structure, so it is usually used in diameter tower cranes, truck mounted cranes etc.