The invention relates to a balancing device for controlling the micro-motion of a welding gun. The balancing device comprises an eccentric mechanism and a balancing mechanism; the eccentric mechanism comprises a cushion block mounted in a way of aligning with a rotating spindle of a driving mechanism and an eccentric block eccentrically connected with the cushion block; the balancing mechanism is mounted on the eccentric block in an alignment way and makes rotational motion on a horizontal plane to drive the welding gun on a welding gun fixing mechanism to move to form a circular trace; and the balancing mechanism comprises an upper bearing hub, a horizontal trace plate, several mandrils, several bearing fixing seats, several balancing rods and several balance supporting seats, the upper bearing hub is located in a trace hole of the horizontal trace plate, an upper linear bearing is arranged in the upper bearing hub in a driving way and is connected with the eccentric block in the alignment way through a vertical shaft, one end of each mandril is fixed at the circumferential side of the upper end of the upper bearing hub, the other end of each mandril movably is penetrated in each bearing fixing seat, one end of each balancing rod is vertically fixed at one side of each bearing fixing seat in a way of corresponding to each mandril, each balancing rod is sleeved by a compression spring, the other end of each balancing rod is movably penetrated in each balance supporting seat, and the balance supporting seats are fixed on the horizontal trace plate.