A steel ball separating device comprises a base plate; a rotating disk is mounted on the base plate; multiple groups of material holes are formed in the rotating disk in the radial direction; a material box is mounted above the rotating disk; the material box and the rotating disk are staggered so as to enable one part of the rotating disk to be located outside the material box; a group of discharging openings are formed in the base plate, are located outside the material box and correspond to one group of material holes of the rotating disk; a rotating driving device is arranged below the base plate and comprises a driving disk, a driving air cylinder and a V-shaped block; the rotating disk is provided with a rotating shaft; the driving disk is mounted on the rotating shaft; multiple camrollers are arranged on the driving disk at predetermined beat intervals; the V-shaped block is connected with the output end of the driving air cylinder; and the V-shaped block is driven by the driving air cylinder to push the cam rollers to drive the rotating disk to rotate to enable the multiple groups of material holes to be aligned to the discharging openings sequentially. By the aid of the steel ball separating device, the process for separating steel balls in different sizes can be realized automatically at the high speed, and the steel ball separating device is simple in structure, stable and reliable.